W3C

HTML 5

A vocabulary and associated APIs for HTML and XHTML

W3C Working Draft 10 June 2008

This Version:
http://www.w3.org/TR/2008/WD-html5-20080610/
Latest Published Version:
http://www.w3.org/TR/html5/
Latest Editor's Draft:
http://www.w3.org/html/wg/html5/
Previous Versions:
http://www.w3.org/TR/2008/WD-html5-20080122/
Editors:
Ian Hickson, Google, Inc.
David Hyatt, Apple, Inc.

The content of this document is also available in the following normative format:

The content is also available in the following non-normative format:


Abstract

This specification defines the 5th major revision of the core language of the World Wide Web: the Hypertext Markup Language (HTML). In this version, new features are introduced to help Web application authors, new elements are introduced based on research into prevailing authoring practices, and special attention has been given to defining clear conformance criteria for user agents in an effort to improve interoperability.

Status of this document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the most recently formally published revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

If you wish to make comments regarding this document, please send them to public-html-comments@w3.org (subscribe, archives). All feedback is welcome.

Implementors should be aware that this specification is not stable. Implementors who are not taking part in the discussions are likely to find the specification changing out from under them in incompatible ways. Vendors interested in implementing this specification before it eventually reaches the Candidate Recommendation stage should join the aforementioned mailing lists and take part in the discussions.

The publication of this document by the W3C as a W3C Working Draft does not imply that all of the participants in the W3C HTML working group endorse the contents of the specification. Indeed, for any section of the specification, one can usually find many members of the working group or of the W3C as a whole who object strongly to the current text, the existence of the section at all, or the idea that the working group should even spend time discussing the concept of that section.

The changes made to this draft specification after the 22 January 2008 First Public Working Draft and this 10 June 2008 Working Draft are recorded in the following documents:

The following document is also available; it describes the differences between HTML 5 and the previous major version of the language, HTML 4:

The W3C HTML Working Group is the W3C working group responsible for this specification's progress along the W3C Recommendation track. This specification is the 10 June 2008 Working Draft.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Stability

Different parts of this specification are at different levels of maturity.

Some of the more major known issues are marked like this. There are many other issues that have been raised as well; the issues given in this document are not the only known issues! There are also some spec-wide issues that have not yet been addressed: case-sensitivity is a very poorly handled topic right now, and the firing of events needs to be unified (right now some bubble, some don't, they all use different text to fire events, etc). It would also be nice to unify the rules on downloading content when attributes change (e.g. src attributes) - should they initiate downloads when the element immediately, is inserted in the document, when active scripts end, etc. This matters e.g. if an attribute is set twice in a row (does it hit the network twice).

Table of contents


1. Introduction

This section is non-normative.

The World Wide Web's markup language has always been HTML. HTML was primarily designed as a language for semantically describing scientific documents, although its general design and adaptations over the years has enabled it to be used to describe a number of other types of documents.

The main area that has not been adequately addressed by HTML is a vague subject referred to as Web Applications. This specification attempts to rectify this, while at the same time updating the HTML specifications to address issues raised in the past few years.

1.1 Scope

This section is non-normative.

This specification is limited to providing a semantic-level markup language and associated semantic-level scripting APIs for authoring accessible pages on the Web ranging from static documents to dynamic applications.

The scope of this specification does not include providing mechanisms for media-specific customization of presentation (although default rendering rules for Web browsers are included at the end of this specification, and several mechanisms for hooking into CSS are provided as part of the language).

The scope of this specification does not include documenting every HTML or DOM feature supported by Web browsers. Browsers support many features that are considered to be very bad for accessibility or that are otherwise inappropriate. For example, the blink element is clearly presentational and authors wishing to cause text to blink should instead use CSS.

The scope of this specification is not to describe an entire operating system. In particular, hardware configuration software, image manipulation tools, and applications that users would be expected to use with high-end workstations on a daily basis are out of scope. In terms of applications, this specification is targeted specifically at applications that would be expected to be used by users on an occasional basis, or regularly but from disparate locations, with low CPU requirements. For instance online purchasing systems, searching systems, games (especially multiplayer online games), public telephone books or address books, communications software (e-mail clients, instant messaging clients, discussion software), document editing software, etc.

For sophisticated cross-platform applications, there already exist several proprietary solutions (such as Mozilla's XUL, Adobe's Flash, or Microsoft's Silverlight). These solutions are evolving faster than any standards process could follow, and the requirements are evolving even faster. These systems are also significantly more complicated to specify, and are orders of magnitude more difficult to achieve interoperability with, than the solutions described in this document. Platform-specific solutions for such sophisticated applications (for example the MacOS X Core APIs) are even further ahead.

1.1.1 Relationship to HTML 4.01, XHTML 1.1, DOM2 HTML

This section is non-normative.

This specification represents a new version of the HTML language, along with a new version of the associated DOM2 HTML API. Migration from HTML4 or XHTML1 to the format and APIs described in this specification should in most cases be straightforward, as care has been taken to ensure that backwards-compatibility is retained.

This specification will eventually supplant Web Forms 2.0 as well. [WF2]

1.1.2 Relationship to XHTML2

This section is non-normative.

XHTML2 [XHTML2] defines a new HTML vocabulary with better features for hyperlinks, multimedia content, annotating document edits, rich metadata, declarative interactive forms, and describing the semantics of human literary works such as poems and scientific papers.

However, it lacks elements to express the semantics of many of the non-document types of content often seen on the Web. For instance, forum sites, auction sites, search engines, online shops, and the like, do not fit the document metaphor well, and are not covered by XHTML2.

This specification aims to extend HTML so that it is also suitable in these contexts.

XHTML2 and this specification use different namespaces and therefore can both be implemented in the same XML processor.

1.1.3 Relationship to XUL, Flash, Silverlight, and other proprietary UI languages

This section is non-normative.

This specification is independent of the various proprietary UI languages that various vendors provide. As an open, vendor-neutral language, HTML provides for a solution to the same problems without the risk of vendor lock-in.

1.2 Structure of this specification

This section is non-normative.

This specification is divided into the following important sections:

The DOM
The DOM, or Document Object Model, provides a base for the rest of the specification.
The Semantics
Documents are built from elements. These elements form a tree using the DOM. Each element also has a predefined meaning, which is explained in this section. User agent requirements for how to handle each element are also given, along with rules for authors on how to use the element.
Browsing Contexts
HTML documents do not exist in a vacuum — this section defines many of the features that affect environments that deal with multiple pages, links between pages, and running scripts.
APIs
The Editing APIs: HTML documents can provide a number of mechanisms for users to modify content, which are described in this section.
The Communication APIs: Applications written in HTML often require mechanisms to communicate with remote servers, as well as communicating with other applications from different domains running on the same client.
Repetition Templates: A mechanism to support repeating sections in forms.
The Language Syntax
All of these features would be for naught if they couldn't be represented in a serialized form and sent to other people, and so this section defines the syntax of HTML, along with rules for how to parse HTML.

There are also a couple of appendices, defining rendering rules for Web browsers and listing areas that are out of scope for this specification.

1.2.1 How to read this specification

This specification should be read like all other specifications. First, it should be read cover-to-cover, multiple times. Then, it should be read backwards at least once. Then it should be read by picking random sections from the contents list and following all the cross-references.

1.3 Conformance requirements

All diagrams, examples, and notes in this specification are non-normative, as are all sections explicitly marked non-normative. Everything else in this specification is normative.

The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this document are to be interpreted as described in RFC2119. For readability, these words do not appear in all uppercase letters in this specification. [RFC2119]

Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and abort these steps") are to be interpreted with the meaning of the key word ("must", "should", "may", etc) used in introducing the algorithm.

This specification describes the conformance criteria for user agents (relevant to implementors) and documents (relevant to authors and authoring tool implementors).

There is no implied relationship between document conformance requirements and implementation conformance requirements. User agents are not free to handle non-conformant documents as they please; the processing model described in this specification applies to implementations regardless of the conformity of the input documents.

User agents fall into several (overlapping) categories with different conformance requirements.

Web browsers and other interactive user agents

Web browsers that support XHTML must process elements and attributes from the HTML namespace found in XML documents as described in this specification, so that users can interact with them, unless the semantics of those elements have been overridden by other specifications.

A conforming XHTML processor would, upon finding an XHTML script element in an XML document, execute the script contained in that element. However, if the element is found within an XSLT transformation sheet (assuming the UA also supports XSLT), then the processor would instead treat the script element as an opaque element that forms part of the transform.

Web browsers that support HTML must process documents labeled as text/html as described in this specification, so that users can interact with them.

Non-interactive presentation user agents

User agents that process HTML and XHTML documents purely to render non-interactive versions of them must comply to the same conformance criteria as Web browsers, except that they are exempt from requirements regarding user interaction.

Typical examples of non-interactive presentation user agents are printers (static UAs) and overhead displays (dynamic UAs). It is expected that most static non-interactive presentation user agents will also opt to lack scripting support.

A non-interactive but dynamic presentation UA would still execute scripts, allowing forms to be dynamically submitted, and so forth. However, since the concept of "focus" is irrelevant when the user cannot interact with the document, the UA would not need to support any of the focus-related DOM APIs.

User agents with no scripting support

Implementations that do not support scripting (or which have their scripting features disabled entirely) are exempt from supporting the events and DOM interfaces mentioned in this specification. For the parts of this specification that are defined in terms of an events model or in terms of the DOM, such user agents must still act as if events and the DOM were supported.

Scripting can form an integral part of an application. Web browsers that do not support scripting, or that have scripting disabled, might be unable to fully convey the author's intent.

Conformance checkers

Conformance checkers must verify that a document conforms to the applicable conformance criteria described in this specification. Automated conformance checkers are exempt from detecting errors that require interpretation of the author's intent (for example, while a document is non-conforming if the content of a blockquote element is not a quote, conformance checkers running without the input of human judgement do not have to check that blockquote elements only contain quoted material).

Conformance checkers must check that the input document conforms when parsed without a browsing context (meaning that no scripts are run, and that the parser's scripting flag is disabled), and should also check that the input document conforms when parsed with a browsing context in which scripts execute, and that the scripts never cause non-conforming states to occur other than transiently during script execution itself. (This is only a "SHOULD" and not a "MUST" requirement because it has been proven to be impossible. [HALTINGPROBLEM])

The term "HTML5 validator" can be used to refer to a conformance checker that itself conforms to the applicable requirements of this specification.

XML DTDs cannot express all the conformance requirements of this specification. Therefore, a validating XML processor and a DTD cannot constitute a conformance checker. Also, since neither of the two authoring formats defined in this specification are applications of SGML, a validating SGML system cannot constitute a conformance checker either.

To put it another way, there are three types of conformance criteria:

  1. Criteria that can be expressed in a DTD.
  2. Criteria that cannot be expressed by a DTD, but can still be checked by a machine.
  3. Criteria that can only be checked by a human.

A conformance checker must check for the first two. A simple DTD-based validator only checks for the first class of errors and is therefore not a conforming conformance checker according to this specification.

Data mining tools

Applications and tools that process HTML and XHTML documents for reasons other than to either render the documents or check them for conformance should act in accordance to the semantics of the documents that they process.

A tool that generates document outlines but increases the nesting level for each paragraph and does not increase the nesting level for each section would not be conforming.

Authoring tools and markup generators

Authoring tools and markup generators must generate conforming documents. Conformance criteria that apply to authors also apply to authoring tools, where appropriate.

Authoring tools are exempt from the strict requirements of using elements only for their specified purpose, but only to the extent that authoring tools are not yet able to determine author intent.

For example, it is not conforming to use an address element for arbitrary contact information; that element can only be used for marking up contact information for the author of the document or section. However, since an authoring tool is likely unable to determine the difference, an authoring tool is exempt from that requirement.

In terms of conformance checking, an editor is therefore required to output documents that conform to the same extent that a conformance checker will verify.

When an authoring tool is used to edit a non-conforming document, it may preserve the conformance errors in sections of the document that were not edited during the editing session (i.e. an editing tool is allowed to round-trip erroneous content). However, an authoring tool must not claim that the output is conformant if errors have been so preserved.

Authoring tools are expected to come in two broad varieties: tools that work from structure or semantic data, and tools that work on a What-You-See-Is-What-You-Get media-specific editing basis (WYSIWYG).

The former is the preferred mechanism for tools that author HTML, since the structure in the source information can be used to make informed choices regarding which HTML elements and attributes are most appropriate.

However, WYSIWYG tools are legitimate. WYSIWYG tools should use elements they know are appropriate, and should not use elements that they do not know to be appropriate. This might in certain extreme cases mean limiting the use of flow elements to just a few elements, like div, b, i, and span and making liberal use of the style attribute.

All authoring tools, whether WYSIWYG or not, should make a best effort attempt at enabling users to create well-structured, semantically rich, media-independent content.

Some conformance requirements are phrased as requirements on elements, attributes, methods or objects. Such requirements fall into two categories: those describing content model restrictions, and those describing implementation behavior. The former category of requirements are requirements on documents and authoring tools. The second category are requirements on user agents.

Conformance requirements phrased as algorithms or specific steps may be implemented in any manner, so long as the end result is equivalent. (In particular, the algorithms defined in this specification are intended to be easy to follow, and not intended to be performant.)

User agents may impose implementation-specific limits on otherwise unconstrained inputs, e.g. to prevent denial of service attacks, to guard against running out of memory, or to work around platform-specific limitations.

For compatibility with existing content and prior specifications, this specification describes two authoring formats: one based on XML (referred to as XHTML5), and one using a custom format inspired by SGML (referred to as HTML5). Implementations may support only one of these two formats, although supporting both is encouraged.

XHTML documents (XML documents using elements from the HTML namespace) that use the new features described in this specification and that are served over the wire (e.g. by HTTP) must be sent using an XML MIME type such as application/xml or application/xhtml+xml and must not be served as text/html. [RFC3023]

Such XML documents may contain a DOCTYPE if desired, but this is not required to conform to this specification.

According to the XML specification, XML processors are not guaranteed to process the external DTD subset referenced in the DOCTYPE. This means, for example, that using entity references for characters in XHTML documents is unsafe (except for <, >, &, " and ').

HTML documents, if they are served over the wire (e.g. by HTTP) must be labeled with the text/html MIME type.

The language in this specification assumes that the user agent expands all entity references, and therefore does not include entity reference nodes in the DOM. If user agents do include entity reference nodes in the DOM, then user agents must handle them as if they were fully expanded when implementing this specification. For example, if a requirement talks about an element's child text nodes, then any text nodes that are children of an entity reference that is a child of that element would be used as well. Entity references to unknown entities must be treated as if they contained just an empty text node for the purposes of the algorithms defined in this specification.

1.3.1 Common conformance requirements for APIs exposed to JavaScript

A lot of arrays/lists/collections in this spec assume zero-based indexes but use the term "indexth" liberally. We should define those to be zero-based and be clearer about this.

Unless otherwise specified, if a DOM attribute that is a floating point number type (float) is assigned an Infinity or Not-a-Number value, a NOT_SUPPORTED_ERR exception must be raised.

Unless otherwise specified, if a method with an argument that is a floating point number type (float) is passed an Infinity or Not-a-Number value, a NOT_SUPPORTED_ERR exception must be raised.

Unless otherwise specified, if a method is passed fewer arguments than is defined for that method in its IDL definition, a NOT_SUPPORTED_ERR exception must be raised.

Unless otherwise specified, if a method is passed more arguments than is defined for that method in its IDL definition, the excess arguments must be ignored.

1.3.2 Dependencies

This specification relies on several other underlying specifications.

XML

Implementations that support XHTML5 must support some version of XML, as well as its corresponding namespaces specification, because XHTML5 uses an XML serialization with namespaces. [XML] [XMLNAMES]

XML Base

User agents must follow the rules given by XML Base to resolve relative URIs in HTML and XHTML fragments. That is the mechanism used in this specification for resolving relative URIs in DOM trees. [XMLBASE]

It is possible for xml:base attributes to be present even in HTML fragments, as such attributes can be added dynamically using script. (Such scripts would not be conforming, however, as xml:base attributes as not allowed in HTML documents.)

DOM

Implementations must support some version of DOM Core and DOM Events, because this specification is defined in terms of the DOM, and some of the features are defined as extensions to the DOM Core interfaces. [DOM3CORE] [DOM3EVENTS]

ECMAScript

Implementations that use ECMAScript to implement the APIs defined in this specification must implement them in a manner consistent with the ECMAScript Bindings defined in the Web IDL specification, as this specification uses that specification's terminology. [WebIDL]

Media Queries

Implementations must support some version of the Media Queries language. However, when applying the rules of the Media Queries specification to media queries found in content attributes of HTML elements, user agents must act as if all U+000B LINE TABULATION characters in the attribute were in fact U+0020 SPACE characters. This is required to provide a consistent processing of space characters in HTML. [MQ]

This specification does not require support of any particular network transport protocols, style sheet language, scripting language, or any of the DOM and WebAPI specifications beyond those described above. However, the language described by this specification is biased towards CSS as the styling language, ECMAScript as the scripting language, and HTTP as the network protocol, and several features assume that those languages and protocols are in use.

This specification might have certain additional requirements on character encodings, image formats, audio formats, and video formats in the respective sections.

1.3.3 Features defined in other specifications

Some elements are defined in terms of their DOM textContent attribute. This is an attribute defined on the Node interface in DOM3 Core. [DOM3CORE]

Should textContent be defined differently for dir="" and <bdo>? Should we come up with an alternative to textContent that handles those and other things, like alt=""?

The interface DOMTimeStamp is defined in DOM3 Core. [DOM3CORE]

The term activation behavior is used as defined in the DOM3 Events specification. [DOM3EVENTS] At the time of writing, DOM3 Events hadn't yet been updated to define that phrase.

The rules for handling alternative style sheets are defined in the CSS object model specification. [CSSOM]

See http://dev.w3.org/cvsweb/~checkout~/csswg/cssom/Overview.html?content-type=text/html;%20charset=utf-8

Certain features are defined in terms of CSS <color> values. When the CSS value currentColor is specified in this context, the "computed value of the 'color' property" for the purposes of determining the computed value of the currentColor keyword is the computed value of the 'color' property on the element in question. [CSS3COLOR]

If a canvas gradient's addColorStop() method is called with the currentColor keyword as the color, then the computed value of the 'color' property on the canvas element is the one that is used.

1.4 Terminology

This specification refers to both HTML and XML attributes and DOM attributes, often in the same context. When it is not clear which is being referred to, they are referred to as content attributes for HTML and XML attributes, and DOM attributes for those from the DOM. Similarly, the term "properties" is used for both ECMAScript object properties and CSS properties. When these are ambiguous they are qualified as object properties and CSS properties respectively.

To ease migration from HTML to XHTML, UAs conforming to this specification will place elements in HTML in the http://www.w3.org/1999/xhtml namespace, at least for the purposes of the DOM and CSS. The term "elements in the HTML namespace", or "HTML elements" for short, when used in this specification, thus refers to both HTML and XHTML elements.

Unless otherwise stated, all elements defined or mentioned in this specification are in the http://www.w3.org/1999/xhtml namespace, and all attributes defined or mentioned in this specification have no namespace (they are in the per-element partition).

The term HTML documents is sometimes used in contrast with XML documents to specifically mean documents that were parsed using an HTML parser (as opposed to using an XML parser or created purely through the DOM).

Generally, when the specification states that a feature applies to HTML or XHTML, it also includes the other. When a feature specifically only applies to one of the two languages, it is called out by explicitly stating that it does not apply to the other format, as in "for HTML, ... (this does not apply to XHTML)".

This specification uses the term document to refer to any use of HTML, ranging from short static documents to long essays or reports with rich multimedia, as well as to fully-fledged interactive applications.

For readability, the term URI is used to refer to both ASCII URIs and Unicode IRIs, as those terms are defined by RFC 3986 and RFC 3987 respectively. On the rare occasions where IRIs are not allowed but ASCII URIs are, this is called out explicitly. [RFC3986] [RFC3987]

The term root element, when not explicitly qualified as referring to the document's root element, means the furthest ancestor element node of whatever node is being discussed, or the node itself if it has no ancestors. When the node is a part of the document, then that is indeed the document's root element; however, if the node is not currently part of the document tree, the root element will be an orphaned node.

An element is said to have been inserted into a document when its root element changes and is now the document's root element.

The term tree order means a pre-order, depth-first traversal of DOM nodes involved (through the parentNode/childNodes relationship).

When it is stated that some element or attribute is ignored, or treated as some other value, or handled as if it was something else, this refers only to the processing of the node after it is in the DOM. A user agent must not mutate the DOM in such situations.

When an XML name, such as an attribute or element name, is referred to in the form prefix:localName, as in xml:id or svg:rect, it refers to a name with the local name localName and the namespace given by the prefix, as defined by the following table:

xml
http://www.w3.org/XML/1998/namespace
html
http://www.w3.org/1999/xhtml
svg
http://www.w3.org/2000/svg

For simplicity, terms such as shown, displayed, and visible might sometimes be used when referring to the way a document is rendered to the user. These terms are not meant to imply a visual medium; they must be considered to apply to other media in equivalent ways.

DOM interfaces defined in this specification use Web IDL. User agents must implement these interfaces as defined by the Web IDL specification. [WEBIDL]

The construction "a Foo object", where Foo is actually an interface, is sometimes used instead of the more accurate "an object implementing the interface Foo".

A DOM attribute is said to be getting when its value is being retrieved (e.g. by author script), and is said to be setting when a new value is assigned to it.

If a DOM object is said to be live, then that means that any attributes returning that object must always return the same object (not a new object each time), and the attributes and methods on that object must operate on the actual underlying data, not a snapshot of the data.

The terms fire and dispatch are used interchangeably in the context of events, as in the DOM Events specifications. [DOM3EVENTS]

The term text node refers to any Text node, including CDATASection nodes; specifically, any Node with node type TEXT_NODE (3) or CDATA_SECTION_NODE (4). [DOM3CORE]

The term plugin is used to mean any content handler, typically a third-party content handler, for Web content types that are not supported by the user agent natively, or for content types that do not expose a DOM, that supports rendering the content as part of the user agent's interface.

One example of a plugin would be a PDF viewer that is instantiated in a browsing context when the user navigates to a PDF file. This would count as a plugin regardless of whether the party that implemented the PDF viewer component was the same as that which implemented the user agent itself. However, a PDF viewer application that launches separate from the user agent (as opposed to using the same interface) is not a plugin by this definition.

This specification does not define a mechanism for interacting with plugins, as it is expected to be user-agent- and platform-specific. Some UAs might opt to support a plugin mechanism such as the Netscape Plugin API; others might use remote content converters or have built-in support for certain types. [NPAPI]

Browsers should take extreme care when interacting with external content intended for plugins. When third-party software is run with the same privileges as the user agent itself, vulnerabilities in the third-party software become as dangerous as those in the user agent.

Some of the algorithms in this specification, for historical reasons, require the user agent to pause until some condition has been met. While a user agent is paused, it must ensure that no scripts execute (e.g. no event handlers, no timers, etc). User agents should remain responsive to user input while paused, however, albeit without letting the user interact with Web pages where that would involve invoking any script.

1.4.1 HTML vs XHTML

This section is non-normative.

This specification defines an abstract language for describing documents and applications, and some APIs for interacting with in-memory representations of resources that use this language.

The in-memory representation is known as "DOM5 HTML", or "the DOM" for short.

There are various concrete syntaxes that can be used to transmit resources that use this abstract language, two of which are defined in this specification.

The first such concrete syntax is "HTML5". This is the format recommended for most authors. It is compatible with all legacy Web browsers. If a document is transmitted with the MIME type text/html, then it will be processed as an "HTML5" document by Web browsers.

The second concrete syntax uses XML, and is known as "XHTML5". When a document is transmitted with an XML MIME type, such as application/xhtml+xml, then it is processed by an XML processor by Web browsers, and treated as an "XHTML5" document. Authors are reminded that the processing for XML and HTML differs; in particular, even minor syntax errors will prevent an XML document from being rendered fully, whereas they would be ignored in the "HTML5" syntax.

The "DOM5 HTML", "HTML5", and "XHTML5" representations cannot all represent the same content. For example, namespaces cannot be represented using "HTML5", but they are supported in "DOM5 HTML" and "XHTML5". Similarly, documents that use the noscript feature can be represented using "HTML5", but cannot be represented with "XHTML5" and "DOM5 HTML". Comments that contain the string "-->" can be represented in "DOM5 HTML" but not in "HTML5" and "XHTML5". And so forth.

2. The Document Object Model

The Document Object Model (DOM) is a representation — a model — of a document and its content. [DOM3CORE] The DOM is not just an API; the conformance criteria of HTML implementations are defined, in this specification, in terms of operations on the DOM.

This specification defines the language represented in the DOM by features together called DOM5 HTML. DOM5 HTML consists of DOM Core Document nodes and DOM Core Element nodes, along with text nodes and other content.

Elements in the DOM represent things; that is, they have intrinsic meaning, also known as semantics.

For example, an ol element represents an ordered list.

In addition, documents and elements in the DOM host APIs that extend the DOM Core APIs, providing new features to application developers using DOM5 HTML.

2.1 Documents

Every XML and HTML document in an HTML UA is represented by a Document object. [DOM3CORE]

Document objects are assumed to be XML documents unless they are flagged as being HTML documents when they are created. Whether a document is an HTML document or an XML document affects the behavior of certain APIs, as well as a few CSS rendering rules. [CSS21]

A Document object created by the createDocument() API on the DOMImplementation object is initially an XML document, but can be made into an HTML document by calling document.open() on it.

All Document objects (in user agents implementing this specification) must also implement the HTMLDocument interface, available using binding-specific methods. (This is the case whether or not the document in question is an HTML document or indeed whether it contains any HTML elements at all.) Document objects must also implement the document-level interface of any other namespaces found in the document that the UA supports. For example, if an HTML implementation also supports SVG, then the Document object must implement HTMLDocument and SVGDocument.

Because the HTMLDocument interface is now obtained using binding-specific casting methods instead of simply being the primary interface of the document object, it is no longer defined as inheriting from Document.

interface HTMLDocument {
  // Resource metadata management
  [PutForwards=href] readonly attribute Location location;
  readonly attribute DOMString URL;
           attribute DOMString domain;
  readonly attribute DOMString referrer;
           attribute DOMString cookie;
  readonly attribute DOMString lastModified;
  readonly attribute DOMString compatMode;
           attribute DOMString charset;
  readonly attribute DOMString characterSet;
  readonly attribute DOMString defaultCharset;
  readonly attribute DOMString readyState;

  // DOM tree accessors
           attribute DOMString title;
           attribute DOMString dir;
           attribute HTMLElement body;
  readonly attribute HTMLCollection images;
  readonly attribute HTMLCollection embeds;
  readonly attribute HTMLCollection plugins;
  readonly attribute HTMLCollection links;
  readonly attribute HTMLCollection forms;
  readonly attribute HTMLCollection anchors;
  readonly attribute HTMLCollection scripts;
  NodeList getElementsByName(in DOMString elementName);
  NodeList getElementsByClassName(in DOMString classNames);

  // Dynamic markup insertion
           attribute DOMString innerHTML;
  HTMLDocument open();
  HTMLDocument open(in DOMString type);
  HTMLDocument open(in DOMString type, in DOMString replace);
  Window open(in DOMString url, in DOMString name, in DOMString features);
  Window open(in DOMString url, in DOMString name, in DOMString features, in boolean replace);
  void close();
  void write(in DOMString text);
  void writeln(in DOMString text);

  // Interaction
  readonly attribute Element activeElement;
  boolean hasFocus();

  // Commands
  readonly attribute HTMLCollection commands;

  // Editing
           attribute boolean designMode;
  boolean execCommand(in DOMString commandId);
  boolean execCommand(in DOMString commandId, in boolean showUI);
  boolean execCommand(in DOMString commandId, in boolean showUI, in DOMString value);
  boolean queryCommandEnabled(in DOMString commandId);
  boolean queryCommandIndeterm(in DOMString commandId);
  boolean queryCommandState(in DOMString commandId);
  boolean queryCommandSupported(in DOMString commandId);
  DOMString queryCommandValue(in DOMString commandId);
  Selection getSelection();
};

Since the HTMLDocument interface holds methods and attributes related to a number of disparate features, the members of this interface are described in various different sections.

2.1.1 Security

User agents must raise a security exception whenever any of the members of an HTMLDocument object are accessed by scripts whose effective script origin is not the same as the Document's effective script origin.

2.1.2 Resource metadata management

The URL attribute must return the document's address.

The referrer attribute must return either the URI of the active document of the source browsing context at the time the navigation was started (that is, the page which navigated the browsing context to the current document), or the empty string if there is no such originating page, or if the UA has been configured not to report referrers in this case, or if the navigation was initiated for a hyperlink with a noreferrer keyword.

In the case of HTTP, the referrer DOM attribute will match the Referer (sic) header that was sent when fetching the current page.

Typically user agents are configured to not report referrers in the case where the referrer uses an encrypted protocol and the current page does not (e.g. when navigating from an https: page to an http: page).

The cookie attribute represents the cookies of the resource.

On getting, if the sandboxed origin browsing context flag is set on the browsing context of the document, the user agent must raise a security exception. Otherwise, it must return the same string as the value of the Cookie HTTP header it would include if fetching the resource indicated by the document's address over HTTP, as per RFC 2109 section 4.3.4. [RFC2109]

On setting, if the sandboxed origin browsing context flag is set on the browsing context of the document, the user agent must raise a security exception. Otherwise, the user agent must act as it would when processing cookies if it had just attempted to fetch the document's address over HTTP, and had received a response with a Set-Cookie header whose value was the specified value, as per RFC 2109 sections 4.3.1, 4.3.2, and 4.3.3. [RFC2109]

Since the cookie attribute is accessible across frames, the path restrictions on cookies are only a tool to help manage which cookies are sent to which parts of the site, and are not in any way a security feature.

The lastModified attribute, on getting, must return the date and time of the Document's source file's last modification, in the user's local timezone, in the following format:

  1. The month component of the date.
  2. A U+002F SOLIDUS character ('/').
  3. The day component of the date.
  4. A U+002F SOLIDUS character ('/').
  5. The year component of the date.
  6. A U+0020 SPACE character.
  7. The hours component of the time.
  8. A U+003A COLON character (':').
  9. The minutes component of the time.
  10. A U+003A COLON character (':').
  11. The seconds component of the time.

All the numeric components above, other than the year, must be given as two digits in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE representing the number in base ten, zero-padded if necessary.

The Document's source file's last modification date and time must be derived from relevant features of the networking protocols used, e.g. from the value of the HTTP Last-Modified header of the document, or from metadata in the file system for local files. If the last modification date and time are not known, the attribute must return the string 01/01/1970 00:00:00.

A Document is always set to one of three modes: no quirks mode, the default; quirks mode, used typically for legacy documents; and limited quirks mode, also known as "almost standards" mode. The mode is only ever changed from the default by the HTML parser, based on the presence, absence, or value of the DOCTYPE string.

The compatMode DOM attribute must return the literal string "CSS1Compat" unless the document has been set to quirks mode by the HTML parser, in which case it must instead return the literal string "BackCompat".

As far as parsing goes, the quirks I know of are:

Documents have an associated character encoding. When a Document object is created, the document's character encoding must be initialized to UTF-16. Various algorithms during page loading affect this value, as does the charset setter. [IANACHARSET]

The charset DOM attribute must, on getting, return the preferred MIME name of the document's character encoding. On setting, if the new value is an IANA-registered alias for a character encoding, the document's character encoding must be set to that character encoding. (Otherwise, nothing happens.)

The characterSet DOM attribute must, on getting, return the preferred MIME name of the document's character encoding.

The defaultCharset DOM attribute must, on getting, return the preferred MIME name of a character encoding, possibly the user's default encoding, or an encoding associated with the user's current geographical location, or any arbitrary encoding name.

Each document has a current document readiness. When a Document object is created, it must have its current document readiness set to the string "loading". Various algorithms during page loading affect this value. When the value is set, the user agent must fire a simple event called readystatechanged at the Document object.

The readyState DOM attribute must, on getting, return the current document readiness.

2.2 Elements

The nodes representing HTML elements in the DOM must implement, and expose to scripts, the interfaces listed for them in the relevant sections of this specification. This includes XHTML elements in XML documents, even when those documents are in another context (e.g. inside an XSLT transform).

The basic interface, from which all the HTML elements' interfaces inherit, and which must be used by elements that have no additional requirements, is the HTMLElement interface.

interface HTMLElement : Element {
  // DOM tree accessors
  NodeList getElementsByClassName(in DOMString classNames);

  // dynamic markup insertion
           attribute DOMString innerHTML;

  // metadata attributes
           attribute DOMString id;
           attribute DOMString title;
           attribute DOMString lang;
           attribute DOMString dir;
           attribute DOMString className;
  readonly attribute DOMTokenList classList;
  readonly attribute DOMStringMap dataset;

  // interaction
           attribute boolean irrelevant;
           attribute long tabIndex;
  void click();
  void focus();
  void blur();
  void scrollIntoView();
  void scrollIntoView(in boolean top);

  // commands
           attribute HTMLMenuElement contextMenu;

  // editing
           attribute boolean draggable;
           attribute DOMString contentEditable;
  readonly attribute DOMString isContentEditable;

  // styling
  readonly attribute CSSStyleDeclaration style;

  // data templates
           attribute DOMString template;
  readonly attribute HTMLDataTemplateElement templateElement;
           attribute DOMString ref;
  readonly attribute Node refNode;
           attribute DOMString registrationMark;
  readonly attribute DocumentFragment originalContent;

  // event handler DOM attributes
           attribute EventListener onabort;
           attribute EventListener onbeforeunload;
           attribute EventListener onblur;
           attribute EventListener onchange;
           attribute EventListener onclick;
           attribute EventListener oncontextmenu;
           attribute EventListener ondblclick;
           attribute EventListener ondrag;
           attribute EventListener ondragend;
           attribute EventListener ondragenter;
           attribute EventListener ondragleave;
           attribute EventListener ondragover;
           attribute EventListener ondragstart;
           attribute EventListener ondrop;
           attribute EventListener onerror;
           attribute EventListener onfocus;
           attribute EventListener onkeydown;
           attribute EventListener onkeypress;
           attribute EventListener onkeyup;
           attribute EventListener onload;
           attribute EventListener onmessage;
           attribute EventListener onmousedown;
           attribute EventListener onmousemove;
           attribute EventListener onmouseout;
           attribute EventListener onmouseover;
           attribute EventListener onmouseup;
           attribute EventListener onmousewheel;
           attribute EventListener onresize;
           attribute EventListener onscroll;
           attribute EventListener onselect;
           attribute EventListener onstorage;
           attribute EventListener onsubmit;
           attribute EventListener onunload;

};

As with the HTMLDocument interface, the HTMLElement interface holds methods and attributes related to a number of disparate features, and the members of this interface are therefore described in various different sections of this specification.

2.2.1 Reflecting content attributes in DOM attributes

Some DOM attributes are defined to reflect a particular content attribute. This means that on getting, the DOM attribute returns the current value of the content attribute, and on setting, the DOM attribute changes the value of the content attribute to the given value.

If a reflecting DOM attribute is a DOMString attribute whose content attribute is defined to contain a URI, then on getting, the DOM attribute must return the value of the content attribute, resolved to an absolute URI, and on setting, must set the content attribute to the specified literal value. If the content attribute is absent, the DOM attribute must return the default value, if the content attribute has one, or else the empty string.

If a reflecting DOM attribute is a DOMString attribute whose content attribute is defined to contain one or more URIs, then on getting, the DOM attribute must split the content attribute on spaces and return the concatenation of each token URI, resolved to an absolute URI, with a single U+0020 SPACE character between each URI; if the content attribute is absent, the DOM attribute must return the default value, if the content attribute has one, or else the empty string. On setting, the DOM attribute must set the content attribute to the specified literal value.

If a reflecting DOM attribute is a DOMString whose content attribute is an enumerated attribute, and the DOM attribute is limited to only known values, then, on getting, the DOM attribute must return the conforming value associated with the state the attribute is in (in its canonical case), or the empty string if the attribute is in a state that has no associated keyword value; and on setting, if the new value case-insensitively matches one of the keywords given for that attribute, then the content attribute must be set to the conforming value associated with the state that the attribute would be in if set to the given new value, otherwise, if the new value is the empty string, then the content attribute must be removed, otherwise, the setter must raise a SYNTAX_ERR exception.

If a reflecting DOM attribute is a DOMString but doesn't fall into any of the above categories, then the getting and setting must be done in a transparent, case-preserving manner.

If a reflecting DOM attribute is a boolean attribute, then on getting the DOM attribute must return true if the attribute is set, and false if it is absent. On setting, the content attribute must be removed if the DOM attribute is set to false, and must be set to have the same value as its name if the DOM attribute is set to true. (This corresponds to the rules for boolean content attributes.)

If a reflecting DOM attribute is a signed integer type (long) then, on getting, the content attribute must be parsed according to the rules for parsing signed integers, and if that is successful, the resulting value must be returned. If, on the other hand, it fails, or if the attribute is absent, then the default value must be returned instead, or 0 if there is no default value. On setting, the given value must be converted to the shortest possible string representing the number as a valid integer in base ten and then that string must be used as the new content attribute value.

If a reflecting DOM attribute is an unsigned integer type (unsigned long) then, on getting, the content attribute must be parsed according to the rules for parsing unsigned integers, and if that is successful, the resulting value must be returned. If, on the other hand, it fails, or if the attribute is absent, the default value must be returned instead, or 0 if there is no default value. On setting, the given value must be converted to the shortest possible string representing the number as a valid non-negative integer in base ten and then that string must be used as the new content attribute value.

If a reflecting DOM attribute is an unsigned integer type (unsigned long) that is limited to only positive non-zero numbers, then the behavior is similar to the previous case, but zero is not allowed. On getting, the content attribute must first be parsed according to the rules for parsing unsigned integers, and if that is successful, the resulting value must be returned. If, on the other hand, it fails, or if the attribute is absent, the default value must be returned instead, or 1 if there is no default value. On setting, if the value is zero, the user agent must fire an INDEX_SIZE_ERR exception. Otherwise, the given value must be converted to the shortest possible string representing the number as a valid non-negative integer in base ten and then that string must be used as the new content attribute value.

If a reflecting DOM attribute is a floating point number type (float) and the content attribute is defined to contain a time offset, then, on getting, the content attribute must be parsed according to the rules for parsing time offsets, and if that is successful, the resulting value, in seconds, must be returned. If that fails, or if the attribute is absent, the default value must be returned, or the not-a-number value (NaN) if there is no default value. On setting, the given value, interpreted as a time offset in seconds, must be converted to a string using the time offset serialization rules, and that string must be used as the new content attribute value.

If a reflecting DOM attribute is a floating point number type (float) and it doesn't fall into one of the earlier categories, then, on getting, the content attribute must be parsed according to the rules for parsing floating point number values, and if that is successful, the resulting value must be returned. If, on the other hand, it fails, or if the attribute is absent, the default value must be returned instead, or 0.0 if there is no default value. On setting, the given value must be converted to the shortest possible string representing the number as a valid floating point number in base ten and then that string must be used as the new content attribute value.

If a reflecting DOM attribute is of the type DOMTokenList, then on getting it must return a DOMTokenList object whose underlying string is the element's corresponding content attribute. When the DOMTokenList object mutates its underlying string, the content attribute must itself be immediately mutated. When the attribute is absent, then the string represented by the DOMTokenList object is the empty string; when the object mutates this empty string, the user agent must first add the corresponding content attribute, and then mutate that attribute instead. DOMTokenList attributes are always read-only. The same DOMTokenList object must be returned every time for each attribute.

If a reflecting DOM attribute has the type HTMLElement, or an interface that descends from HTMLElement, then, on getting, it must run the following algorithm (stopping at the first point where a value is returned):

  1. If the corresponding content attribute is absent, then the DOM attribute must return null.
  2. Let candidate be the element that the document.getElementById() method would find if it was passed as its argument the current value of the corresponding content attribute.
  3. If candidate is null, or if it is not type-compatible with the DOM attribute, then the DOM attribute must return null.
  4. Otherwise, it must return candidate.

On setting, if the given element has an id attribute, then the content attribute must be set to the value of that id attribute. Otherwise, the DOM attribute must be set to the empty string.

2.3 Common DOM interfaces

2.3.1 Collections

The HTMLCollection, HTMLFormControlsCollection, and HTMLOptionsCollection interfaces represent various lists of DOM nodes. Collectively, objects implementing these interfaces are called collections.

When a collection is created, a filter and a root are associated with the collection.

For example, when the HTMLCollection object for the document.images attribute is created, it is associated with a filter that selects only img elements, and rooted at the root of the document.

The collection then represents a live view of the subtree rooted at the collection's root, containing only nodes that match the given filter. The view is linear. In the absence of specific requirements to the contrary, the nodes within the collection must be sorted in tree order.

The rows list is not in tree order.

An attribute that returns a collection must return the same object every time it is retrieved.

2.3.1.1. HTMLCollection

The HTMLCollection interface represents a generic collection of elements.

interface HTMLCollection {
  readonly attribute unsigned long length;
  [IndexGetter] Element item(in unsigned long index);
  [NameGetter] Element namedItem(in DOMString name);
};

The length attribute must return the number of nodes represented by the collection.

The item(index) method must return the indexth node in the collection. If there is no indexth node in the collection, then the method must return null.

The namedItem(key) method must return the first node in the collection that matches the following requirements:

If no such elements are found, then the method must return null.

2.3.1.2. HTMLFormControlsCollection

The HTMLFormControlsCollection interface represents a collection of form controls.

interface HTMLFormControlsCollection {
  readonly attribute unsigned long length;
  [IndexGetter] HTMLElement item(in unsigned long index);
  [NameGetter] Object namedItem(in DOMString name);
};

The length attribute must return the number of nodes represented by the collection.

The item(index) method must return the indexth node in the collection. If there is no indexth node in the collection, then the method must return null.

The namedItem(key) method must act according to the following algorithm:

  1. If, at the time the method is called, there is exactly one node in the collection that has either an id attribute or a name attribute equal to key, then return that node and stop the algorithm.
  2. Otherwise, if there are no nodes in the collection that have either an id attribute or a name attribute equal to key, then return null and stop the algorithm.
  3. Otherwise, create a NodeList object representing a live view of the HTMLFormControlsCollection object, further filtered so that the only nodes in the NodeList object are those that have either an id attribute or a name attribute equal to key. The nodes in the NodeList object must be sorted in tree order.
  4. Return that NodeList object.
2.3.1.3. HTMLOptionsCollection

The HTMLOptionsCollection interface represents a list of option elements.

interface HTMLOptionsCollection {
           attribute unsigned long length;
  [IndexGetter] HTMLOptionElement item(in unsigned long index);
  [NameGetter] Object namedItem(in DOMString name);
};

On getting, the length attribute must return the number of nodes represented by the collection.

On setting, the behavior depends on whether the new value is equal to, greater than, or less than the number of nodes represented by the collection at that time. If the number is the same, then setting the attribute must do nothing. If the new value is greater, then n new option elements with no attributes and no child nodes must be appended to the select element on which the HTMLOptionsCollection is rooted, where n is the difference between the two numbers (new value minus old value). If the new value is lower, then the last n nodes in the collection must be removed from their parent nodes, where n is the difference between the two numbers (old value minus new value).

Setting length never removes or adds any optgroup elements, and never adds new children to existing optgroup elements (though it can remove children from them).

The item(index) method must return the indexth node in the collection. If there is no indexth node in the collection, then the method must return null.

The namedItem(key) method must act according to the following algorithm:

  1. If, at the time the method is called, there is exactly one node in the collection that has either an id attribute or a name attribute equal to key, then return that node and stop the algorithm.
  2. Otherwise, if there are no nodes in the collection that have either an id attribute or a name attribute equal to key, then return null and stop the algorithm.
  3. Otherwise, create a NodeList object representing a live view of the HTMLOptionsCollection object, further filtered so that the only nodes in the NodeList object are those that have either an id attribute or a name attribute equal to key. The nodes in the NodeList object must be sorted in tree order.
  4. Return that NodeList object.

We may want to add add() and remove() methods here too because IE implements HTMLSelectElement and HTMLOptionsCollection on the same object, and so people use them almost interchangeably in the wild.

2.3.2 DOMTokenList

The DOMTokenList interface represents an interface to an underlying string that consists of an unordered set of unique space-separated tokens.

Which string underlies a particular DOMTokenList object is defined when the object is created. It might be a content attribute (e.g. the string that underlies the classList object is the class attribute), or it might be an anonymous string (e.g. when a DOMTokenList object is passed to an author-implemented callback in the datagrid APIs).

[Stringifies] interface DOMTokenList {
  readonly attribute unsigned long length;
  [IndexGetter] DOMString item(in unsigned long index);
  boolean has(in DOMString token);
  void add(in DOMString token);
  void remove(in DOMString token);
  boolean toggle(in DOMString token);
};

The length attribute must return the number of unique tokens that result from splitting the underlying string on spaces.

The item(index) method must split the underlying string on spaces, sort the resulting list of tokens by Unicode codepoint, remove exact duplicates, and then return the indexth item in this list. If index is equal to or greater than the number of tokens, then the method must return null.

The has(token) method must run the following algorithm:

  1. If the token argument contains any spaces, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  2. Otherwise, split the underlying string on spaces to get the list of tokens in the object's underlying string.
  3. If the token indicated by token is one of the tokens in the object's underlying string then return true and stop this algorithm.
  4. Otherwise, return false.

The add(token) method must run the following algorithm:

  1. If the token argument contains any spaces, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  2. Otherwise, split the underlying string on spaces to get the list of tokens in the object's underlying string.
  3. If the given token is already one of the tokens in the DOMTokenList object's underlying string then stop the algorithm.
  4. Otherwise, if the DOMTokenList object's underlying string is not the empty string and the last character of that string is not a space character, then append a U+0020 SPACE character to the end of that string.
  5. Append the value of token to the end of the DOMTokenList object's underlying string.

The remove(token) method must run the following algorithm:

  1. If the token argument contains any spaces, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  2. Otherwise, remove the given token from the underlying string.

The toggle(token) method must run the following algorithm:

  1. If the token argument contains any spaces, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  2. Otherwise, split the underlying string on spaces to get the list of tokens in the object's underlying string.
  3. If the given token is already one of the tokens in the DOMTokenList object's underlying string then remove the given token from the underlying string, and stop the algorithm, returning false.
  4. Otherwise, if the DOMTokenList object's underlying string is not the empty string and the last character of that string is not a space character, then append a U+0020 SPACE character to the end of that string.
  5. Append the value of token to the end of the DOMTokenList object's underlying string.
  6. Return true.

Objects implementing the DOMTokenList interface must stringify to the object's underlying string representation.

2.3.3 DOMStringMap

The DOMStringMap interface represents a set of name-value pairs. When a DOMStringMap object is instanced, it is associated with three algorithms, one for getting values from names, one for setting names to certain values, and one for deleting names.

The names of the methods on this interface are temporary and will be fixed when the Web IDL / "Language Bindings for DOM Specifications" spec is ready to handle this case.

interface DOMStringMap {
  [NameGetter] DOMString XXX1(in DOMString name); 
  [NameSetter] void XXX2(in DOMString name, in DOMString value); 
  [XXX] boolean XXX3(in DOMString name); 
};

The XXX1(name) method must call the algorithm for getting values from names, passing name as the name, and must return the corresponding value, or null if name has no corresponding value.

The XXX2(name, value) method must call the algorithm for setting names to certain values, passing name as the name and value as the value.

The XXX3(name) method must call the algorithm for deleting names, passing name as the name, and must return true.

2.3.4 DOM feature strings

DOM3 Core defines mechanisms for checking for interface support, and for obtaining implementations of interfaces, using feature strings. [DOM3CORE]

A DOM application can use the hasFeature(feature, version) method of the DOMImplementation interface with parameter values "HTML" and "5.0" (respectively) to determine whether or not this module is supported by the implementation. In addition to the feature string "HTML", the feature string "XHTML" (with version string "5.0") can be used to check if the implementation supports XHTML. User agents should respond with a true value when the hasFeature method is queried with these values. Authors are cautioned, however, that UAs returning true might not be perfectly compliant, and that UAs returning false might well have support for features in this specification; in general, therefore, use of this method is discouraged.

The values "HTML" and "XHTML" (both with version "5.0") should also be supported in the context of the getFeature() and isSupported() methods, as defined by DOM3 Core.

The interfaces defined in this specification are not always supersets of the interfaces defined in DOM2 HTML; some features that were formerly deprecated, poorly supported, rarely used or considered unnecessary have been removed. Therefore it is not guaranteed that an implementation that supports "HTML" "5.0" also supports "HTML" "2.0".

2.4 DOM tree accessors

The html element of a document is the document's root element, if there is one and it's an html element, or null otherwise.

The head element of a document is the first head element that is a child of the html element, if there is one, or null otherwise.

The title element of a document is the first title element in the document (in tree order), if there is one, or null otherwise.

The title attribute must, on getting, run the following algorithm:

  1. If the root element is an svg element in the "http://www.w3.org/2000/svg" namespace, and the user agent supports SVG, then the getter must return the value that would have been returned by the DOM attribute of the same name on the SVGDocument interface.

  2. Otherwise, it must return a concatenation of the data of all the child text nodes of the title element, in tree order, or the empty string if the title element is null.

On setting, the following algorithm must be run:

  1. If the root element is an svg element in the "http://www.w3.org/2000/svg" namespace, and the user agent supports SVG, then the setter must defer to the setter for the DOM attribute of the same name on the SVGDocument interface. Stop the algorithm here.

  2. If the title element is null and the head element is null, then the attribute must do nothing. Stop the algorithm here.
  3. If the title element is null, then a new title element must be created and appended to the head element.
  4. The children of the title element (if any) must all be removed.
  5. A single Text node whose data is the new value being assigned must be appended to the title element.

The title attribute on the HTMLDocument interface should shadow the attribute of the same name on the SVGDocument interface when the user agent supports both HTML and SVG.

The body element of a document is the first child of the html element that is either a body element or a frameset element. If there is no such element, it is null. If the body element is null, then when the specification requires that events be fired at "the body element", they must instead be fired at the Document object.

The body attribute, on getting, must return the body element of the document (either a body element, a frameset element, or null). On setting, the following algorithm must be run:

  1. If the new value is not a body or frameset element, then raise a HIERARCHY_REQUEST_ERR exception and abort these steps.
  2. Otherwise, if the new value is the same as the body element, do nothing. Abort these steps.
  3. Otherwise, if the body element is not null, then replace that element with the new value in the DOM, as if the root element's replaceChild() method had been called with the new value and the incumbent body element as its two arguments respectively, then abort these steps.
  4. Otherwise, the the body element is null. Append the new value to the root element.

The images attribute must return an HTMLCollection rooted at the Document node, whose filter matches only img elements.

The embeds attribute must return an HTMLCollection rooted at the Document node, whose filter matches only embed elements.

The plugins attribute must return the same object as that returned by the embeds attribute.

The links attribute must return an HTMLCollection rooted at the Document node, whose filter matches only a elements with href attributes and area elements with href attributes.

The forms attribute must return an HTMLCollection rooted at the Document node, whose filter matches only form elements.

The anchors attribute must return an HTMLCollection rooted at the Document node, whose filter matches only a elements with name attributes.

The scripts attribute must return an HTMLCollection rooted at the Document node, whose filter matches only script elements.

The getElementsByName(name) method a string name, and must return a live NodeList containing all the a, applet, button, form, iframe, img, input, map, meta, object, select, and textarea elements in that document that have a name attribute whose value is equal to the name argument.

The getElementsByClassName(classNames) method takes a string that contains an unordered set of unique space-separated tokens representing classes. When called, the method must return a live NodeList object containing all the elements in the document that have all the classes specified in that argument, having obtained the classes by splitting a string on spaces. If there are no tokens specified in the argument, then the method must return an empty NodeList.

The getElementsByClassName() method on the HTMLElement interface must return a live NodeList with the nodes that the HTMLDocument getElementsByClassName() method would return when passed the same argument(s), excluding any elements that are not descendants of the HTMLElement object on which the method was invoked.

HTML, SVG, and MathML elements define which classes they are in by having an attribute in the per-element partition with the name class containing a space-separated list of classes to which the element belongs. Other specifications may also allow elements in their namespaces to be labeled as being in specific classes. UAs must not assume that all attributes of the name class for elements in any namespace work in this way, however, and must not assume that such attributes, when used as global attributes, label other elements as being in specific classes.

Given the following XHTML fragment:

<div id="example">
 <p id="p1" class="aaa bbb"/>
 <p id="p2" class="aaa ccc"/>
 <p id="p3" class="bbb ccc"/>
</div>

A call to document.getElementById('example').getElementsByClassName('aaa') would return a NodeList with the two paragraphs p1 and p2 in it.

A call to getElementsByClassName('ccc bbb') would only return one node, however, namely p3. A call to document.getElementById('example').getElementsByClassName('bbb  ccc ') would return the same thing.

A call to getElementsByClassName('aaa,bbb') would return no nodes; none of the elements above are in the "aaa,bbb" class.

The dir attribute on the HTMLDocument interface is defined along with the dir content attribute.

2.5 Dynamic markup insertion

The document.write() family of methods and the innerHTML family of DOM attributes enable script authors to dynamically insert markup into the document.

bz argues that innerHTML should be called something else on XML documents and XML elements. Is the sanity worth the migration pain?

Because these APIs interact with the parser, their behavior varies depending on whether they are used with HTML documents (and the HTML parser) or XHTML in XML documents (and the XML parser). The following table cross-references the various versions of these APIs.

document.write() innerHTML
For documents that are HTML documents document.write() in HTML innerHTML in HTML
For documents that are XML documents document.write() in XML innerHTML in XML

Regardless of the parsing mode, the document.writeln(...) method must call the document.write() method with the same argument(s), and then call the document.write() method with, as its argument, a string consisting of a single line feed character (U+000A).

2.5.1 Controlling the input stream

The open() method comes in several variants with different numbers of arguments.

When called with two or fewer arguments, the method must act as follows:

  1. Let type be the value of the first argument, if there is one, or "text/html" otherwise.

  2. Let replace be true if there is a second argument and it has the value "replace", and false otherwise.

  3. If the document has an active parser that isn't a script-created parser, and the insertion point associated with that parser's input stream is not undefined (that is, it does point to somewhere in the input stream), then the method does nothing. Abort these steps and return the Document object on which the method was invoked.

    This basically causes document.open() to be ignored when it's called in an inline script found during the parsing of data sent over the network, while still letting it have an effect when called asynchronously or on a document that is itself being spoon-fed using these APIs.

  4. onbeforeunload, onunload, reset timers, empty event queue, kill any pending transactions, XMLHttpRequests, etc

  5. If the document has an active parser, then stop that parser, and throw away any pending content in the input stream. what about if it doesn't, because it's either like a text/plain, or Atom, or PDF, or XHTML, or image document, or something?

  6. Remove all child nodes of the document.

  7. Change the document's character encoding to UTF-16.

  8. Create a new HTML parser and associate it with the document. This is a script-created parser (meaning that it can be closed by the document.open() and document.close() methods, and that the tokeniser will wait for an explicit call to document.close() before emitting an end-of-file token).

  9. Mark the document as being an HTML document (it might already be so-marked).
  10. If type does not have the value "text/html", then act as if the tokeniser had emitted a pre element start tag, then set the HTML parser's tokenisation stage's content model flag to PLAINTEXT.

  11. If replace is false, then:

    1. Remove all the entries in the browsing context's session history after the current entry in its Document's History object
    2. Remove any earlier entries that share the same Document
    3. Add a new entry just before the last entry that is associated with the text that was parsed by the previous parser associated with the Document object, as well as the state of the document at the start of these steps. (This allows the user to step backwards in the session history to see the page before it was blown away by the document.open() call.)
  12. Finally, set the insertion point to point at just before the end of the input stream (which at this point will be empty).

  13. Return the Document on which the method was invoked.

We shouldn't hard-code text/plain there. We should do it some other way, e.g. hand off to the section on content-sniffing and handling of incoming data streams, the part that defines how this all works when stuff comes over the network.

When called with three or more arguments, the open() method on the HTMLDocument object must call the open() method on the Window interface of the object returned by the defaultView attribute of the DocumentView interface of the HTMLDocument object, with the same arguments as the original call to the open() method, and return whatever that method returned. If the defaultView attribute of the DocumentView interface of the HTMLDocument object is null, then the method must raise an INVALID_ACCESS_ERR exception.

The close() method must do nothing if there is no script-created parser associated with the document. If there is such a parser, then, when the method is called, the user agent must insert an explicit "EOF" character at the insertion point of the parser's input stream.

2.5.2 Dynamic markup insertion in HTML

In HTML, the document.write(...) method must act as follows:

  1. If the insertion point is undefined, the open() method must be called (with no arguments) on the document object. The insertion point will point at just before the end of the (empty) input stream.

  2. The string consisting of the concatenation of all the arguments to the method must be inserted into the input stream just before the insertion point.

  3. If there is a script that will execute as soon as the parser resumes, then the method must now return without further processing of the input stream.

  4. Otherwise, the tokeniser must process the characters that were inserted, one at a time, processing resulting tokens as they are emitted, and stopping when the tokeniser reaches the insertion point or when the processing of the tokeniser is aborted by the tree construction stage (this can happen if a script start tag token is emitted by the tokeniser).

    If the document.write() method was called from script executing inline (i.e. executing because the parser parsed a set of script tags), then this is a reentrant invocation of the parser.

  5. Finally, the method must return.

In HTML, the innerHTML DOM attribute of all HTMLElement and HTMLDocument nodes returns a serialization of the node's children using the HTML syntax. On setting, it replaces the node's children with new nodes that result from parsing the given value. The formal definitions follow.

On getting, the innerHTML DOM attribute must return the result of running the HTML fragment serialization algorithm on the node.

On setting, if the node is a document, the innerHTML DOM attribute must run the following algorithm:

  1. If the document has an active parser, then stop that parser, and throw away any pending content in the input stream. what about if it doesn't, because it's either like a text/plain, or Atom, or PDF, or XHTML, or image document, or something?

  2. Remove the children nodes of the Document whose innerHTML attribute is being set.

  3. Create a new HTML parser, in its initial state, and associate it with the Document node.

  4. Place into the input stream for the HTML parser just created the string being assigned into the innerHTML attribute.

  5. Start the parser and let it run until it has consumed all the characters just inserted into the input stream. (The Document node will have been populated with elements and a load event will have fired on its body element.)

Otherwise, if the node is an element, then setting the innerHTML DOM attribute must cause the following algorithm to run instead:

  1. Invoke the HTML fragment parsing algorithm, with the element whose innerHTML attribute is being set as the context element, and the string being assigned into the innerHTML attribute as the input. Let new children be the result of this algorithm.

  2. Remove the children of the element whose innerHTML attribute is being set.

  3. Let target document be the ownerDocument of the Element node whose innerHTML attribute is being set.

  4. Set the ownerDocument of all the nodes in new children to the target document.

  5. Append all the new children nodes to the node whose innerHTML attribute is being set, preserving their order.

script elements inserted using innerHTML do not execute when they are inserted.

2.5.3 Dynamic markup insertion in XML

In an XML context, the document.write() method must raise an INVALID_ACCESS_ERR exception.

On the other hand, however, the innerHTML attribute is indeed usable in an XML context.

In an XML context, the innerHTML DOM attribute on HTMLElements must return a string in the form of an internal general parsed entity, and on HTMLDocuments must return a string in the form of a document entity. The string returned must be XML namespace-well-formed and must be an isomorphic serialization of all of that node's child nodes, in document order. User agents may adjust prefixes and namespace declarations in the serialization (and indeed might be forced to do so in some cases to obtain namespace-well-formed XML). If any of the elements in the serialization are in no namespace, the default namespace in scope for those elements must be explicitly declared as the empty string. [XML] [XMLNS]

If any of the following cases are found in the DOM being serialized, the user agent must raise an INVALID_STATE_ERR exception:

These are the only ways to make a DOM unserializable. The DOM enforces all the other XML constraints; for example, trying to set an attribute with a name that contains an equals sign (=) will raised an INVALID_CHARACTER_ERR exception.

On setting, in an XML context, the innerHTML DOM attribute on HTMLElements and HTMLDocuments must run the following algorithm:

  1. The user agent must create a new XML parser.

  2. If the innerHTML attribute is being set on an element, the user agent must feed the parser just created the string corresponding to the start tag of that element, declaring all the namespace prefixes that are in scope on that element in the DOM, as well as declaring the default namespace (if any) that is in scope on that element in the DOM.

  3. The user agent must feed the parser just created the string being assigned into the innerHTML attribute.

  4. If the innerHTML attribute is being set on an element, the user agent must feed the parser the string corresponding to the end tag of that element.

  5. If the parser found a well-formedness error, the attribute's setter must raise a SYNTAX_ERR exception and abort these steps.

  6. The user agent must remove the children nodes of the node whose innerHTML attribute is being set.

  7. If the attribute is being set on a Document node, let new children be the children of the document, preserving their order. Otherwise, the attribute is being set on an Element node; let new children be the children of the document's root element, preserving their order.

  8. If the attribute is being set on a Document node, let target document be that Document node. Otherwise, the attribute is being set on an Element node; let target document be the ownerDocument of that Element.

  9. Set the ownerDocument of all the nodes in new children to the target document.

  10. Append all the new children nodes to the node whose innerHTML attribute is being set, preserving their order.

script elements inserted using innerHTML do not execute when they are inserted.

2.6 APIs in HTML documents

For HTML documents, and for HTML elements in HTML documents, certain APIs defined in DOM3 Core become case-insensitive or case-changing, as sometimes defined in DOM3 Core, and as summarized or required below. [DOM3CORE].

This does not apply to XML documents or to elements that are not in the HTML namespace despite being in HTML documents.

Element.tagName, Node.nodeName, and Node.localName

These attributes return tag names in all uppercase and attribute names in all lowercase, regardless of the case with which they were created.

Document.createElement()

The canonical form of HTML markup is all-lowercase; thus, this method will lowercase the argument before creating the requisite element. Also, the element created must be in the HTML namespace.

This doesn't apply to Document.createElementNS(). Thus, it is possible, by passing this last method a tag name in the wrong case, to create an element that claims to have the tag name of an element defined in this specification, but doesn't support its interfaces, because it really has another tag name not accessible from the DOM APIs.

Element.setAttributeNode()

When an Attr node is set on an HTML element, it must have its name lowercased before the element is affected.

This doesn't apply to Document.setAttributeNodeNS().

Element.setAttribute()

When an attribute is set on an HTML element, the name argument must be lowercased before the element is affected.

This doesn't apply to Document.setAttributeNS().

Document.getElementsByTagName() and Element.getElementsByTagName()

These methods (but not their namespaced counterparts) must compare the given argument case-insensitively when looking at HTML elements, and case-sensitively otherwise.

Thus, in an HTML document with nodes in multiple namespaces, these methods will be both case-sensitive and case-insensitive at the same time.

Document.renameNode()

If the new namespace is the HTML namespace, then the new qualified name must be lowercased before the rename takes place.

3. Semantics and structure of HTML elements

3.1 Introduction

This section is non-normative.

An introduction to marking up a document.

3.2 Common microsyntaxes

There are various places in HTML that accept particular data types, such as dates or numbers. This section describes what the conformance criteria for content in those formats is, and how to parse them.

Need to go through the whole spec and make sure all the attribute values are clearly defined either in terms of microsyntaxes or in terms of other specs, or as "Text" or some such.

3.2.1 Common parser idioms

The space characters, for the purposes of this specification, are U+0020 SPACE, U+0009 CHARACTER TABULATION (tab), U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM FEED (FF), and U+000D CARRIAGE RETURN (CR).

Some of the micro-parsers described below follow the pattern of having an input variable that holds the string being parsed, and having a position variable pointing at the next character to parse in input.

For parsers based on this pattern, a step that requires the user agent to collect a sequence of characters means that the following algorithm must be run, with characters being the set of characters that can be collected:

  1. Let input and position be the same variables as those of the same name in the algorithm that invoked these steps.

  2. Let result be the empty string.

  3. While position doesn't point past the end of input and the character at position is one of the characters, append that character to the end of result and advance position to the next character in input.

  4. Return result.

The step skip whitespace means that the user agent must collect a sequence of characters that are space characters. The step skip Zs characters means that the user agent must collect a sequence of characters that are in the Unicode character class Zs. In both cases, the collected characters are not used. [UNICODE]

3.2.2 Boolean attributes

A number of attributes in HTML5 are boolean attributes. The presence of a boolean attribute on an element represents the true value, and the absence of the attribute represents the false value.

If the attribute is present, its value must either be the empty string or a value that is a case-insensitive match for the attribute's canonical name, with no leading or trailing whitespace.

3.2.3 Numbers

3.2.3.1. Unsigned integers

A string is a valid non-negative integer if it consists of one of more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9).

The rules for parsing non-negative integers are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will either return zero, a positive integer, or an error. Leading spaces are ignored. Trailing spaces and indeed any trailing garbage characters are ignored.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let value have the value 0.

  4. Skip whitespace.

  5. If position is past the end of input, return an error.

  6. If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.

  7. If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9):

    1. Multiply value by ten.
    2. Add the value of the current character (0..9) to value.
    3. Advance position to the next character.
    4. If position is not past the end of input, return to the top of step 7 in the overall algorithm (that's the step within which these substeps find themselves).
  8. Return value.

3.2.3.2. Signed integers

A string is a valid integer if it consists of one of more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), optionally prefixed with a U+002D HYPHEN-MINUS ("-") character.

The rules for parsing integers are similar to the rules for non-negative integers, and are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will either return an integer or an error. Leading spaces are ignored. Trailing spaces and trailing garbage characters are ignored.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let value have the value 0.

  4. Let sign have the value "positive".

  5. Skip whitespace.

  6. If position is past the end of input, return an error.

  7. If the character indicated by position (the first character) is a U+002D HYPHEN-MINUS ("-") character:

    1. Let sign be "negative".
    2. Advance position to the next character.
    3. If position is past the end of input, return an error.
  8. If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.

  9. If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9):

    1. Multiply value by ten.
    2. Add the value of the current character (0..9) to value.
    3. Advance position to the next character.
    4. If position is not past the end of input, return to the top of step 9 in the overall algorithm (that's the step within which these substeps find themselves).
  10. If sign is "positive", return value, otherwise return 0-value.

3.2.3.3. Real numbers

A string is a valid floating point number if it consists of one of more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), optionally with a single U+002E FULL STOP (".") character somewhere (either before these numbers, in between two numbers, or after the numbers), all optionally prefixed with a U+002D HYPHEN-MINUS ("-") character.

The rules for parsing floating point number values are as given in the following algorithm. As with the previous algorithms, when this one is invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will either return a number or an error. Leading spaces are ignored. Trailing spaces and garbage characters are ignored.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let value have the value 0.

  4. Let sign have the value "positive".

  5. Skip whitespace.

  6. If position is past the end of input, return an error.

  7. If the character indicated by position (the first character) is a U+002D HYPHEN-MINUS ("-") character:

    1. Let sign be "negative".
    2. Advance position to the next character.
    3. If position is past the end of input, return an error.
  8. If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9) or U+002E FULL STOP ("."), then return an error.

  9. If the next character is U+002E FULL STOP ("."), but either that is the last character or the character after that one is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.

  10. If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9):

    1. Multiply value by ten.
    2. Add the value of the current character (0..9) to value.
    3. Advance position to the next character.
    4. If position is past the end of input, then if sign is "positive", return value, otherwise return 0-value.
    5. Otherwise return to the top of step 10 in the overall algorithm (that's the step within which these substeps find themselves).
  11. Otherwise, if the next character is not a U+002E FULL STOP ("."), then if sign is "positive", return value, otherwise return 0-value.

  12. The next character is a U+002E FULL STOP ("."). Advance position to the character after that.

  13. Let divisor be 1.

  14. If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9):

    1. Multiply divisor by ten.
    2. Add the value of the current character (0..9) divided by divisor, to value.
    3. Advance position to the next character.
    4. If position is past the end of input, then if sign is "positive", return value, otherwise return 0-value.
    5. Otherwise return to the top of step 14 in the overall algorithm (that's the step within which these substeps find themselves).
  15. Otherwise, if sign is "positive", return value, otherwise return 0-value.

3.2.3.4. Ratios

The algorithms described in this section are used by the progress and meter elements.

A valid denominator punctuation character is one of the characters from the table below. There is a value associated with each denominator punctuation character, as shown in the table below.

Denominator Punctuation Character Value
U+0025 PERCENT SIGN % 100
U+066A ARABIC PERCENT SIGN ٪ 100
U+FE6A SMALL PERCENT SIGN 100
U+FF05 FULLWIDTH PERCENT SIGN 100
U+2030 PER MILLE SIGN 1000
U+2031 PER TEN THOUSAND SIGN 10000

The steps for finding one or two numbers of a ratio in a string are as follows:

  1. If the string is empty, then return nothing and abort these steps.
  2. Find a number in the string according to the algorithm below, starting at the start of the string.
  3. If the sub-algorithm in step 2 returned nothing or returned an error condition, return nothing and abort these steps.
  4. Set number1 to the number returned by the sub-algorithm in step 2.
  5. Starting with the character immediately after the last one examined by the sub-algorithm in step 2, skip any characters in the string that are in the Unicode character class Zs (this might match zero characters). [UNICODE]
  6. If there are still further characters in the string, and the next character in the string is a valid denominator punctuation character, set denominator to that character.
  7. If the string contains any other characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, but denominator was given a value in the step 6, return nothing and abort these steps.
  8. Otherwise, if denominator was given a value in step 6, return number1 and denominator and abort these steps.
  9. Find a number in the string again, starting immediately after the last character that was examined by the sub-algorithm in step 2.
  10. If the sub-algorithm in step 9 returned nothing or an error condition, return nothing and abort these steps.
  11. Set number2 to the number returned by the sub-algorithm in step 9.
  12. If there are still further characters in the string, and the next character in the string is a valid denominator punctuation character, return nothing and abort these steps.
  13. If the string contains any other characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, return nothing and abort these steps.
  14. Otherwise, return number1 and number2.

The algorithm to find a number is as follows. It is given a string and a starting position, and returns either nothing, a number, or an error condition.

  1. Starting at the given starting position, ignore all characters in the given string until the first character that is either a U+002E FULL STOP or one of the ten characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE.
  2. If there are no such characters, return nothing and abort these steps.
  3. Starting with the character matched in step 1, collect all the consecutive characters that are either a U+002E FULL STOP or one of the ten characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, and assign this string of one or more characters to string.
  4. If string contains more than one U+002E FULL STOP character then return an error condition and abort these steps.
  5. Parse string according to the rules for parsing floating point number values, to obtain number. This step cannot fail (string is guaranteed to be a valid floating point number).
  6. Return number.
3.2.3.5. Percentages and dimensions

valid positive non-zero integers rules for parsing dimension values (only used by height/width on img, embed, object — lengths in css pixels or percentages)

3.2.3.6. Lists of integers

A valid list of integers is a number of valid integers separated by U+002C COMMA characters, with no other characters (e.g. no space characters). In addition, there might be restrictions on the number of integers that can be given, or on the range of values allowed.

The rules for parsing a list of integers are as follows:

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let numbers be an initially empty list of integers. This list will be the result of this algorithm.

  4. If there is a character in the string input at position position, and it is either a U+0020 SPACE, U+002C COMMA, or U+003B SEMICOLON character, then advance position to the next character in input, or to beyond the end of the string if there are no more characters.

  5. If position points to beyond the end of input, return numbers and abort.

  6. If the character in the string input at position position is a U+0020 SPACE, U+002C COMMA, or U+003B SEMICOLON character, then return to step 4.

  7. Let negated be false.

  8. Let value be 0.

  9. Let started be false. This variable is set to true when the parser sees a number or a "-" character.

  10. Let got number be false. This variable is set to true when the parser sees a number.

  11. Let finished be false. This variable is set to true to switch parser into a mode where it ignores characters until the next separator.

  12. Let bogus be false.

  13. Parser: If the character in the string input at position position is:

    A U+002D HYPHEN-MINUS character

    Follow these substeps:

    1. If got number is true, let finished be true.
    2. If finished is true, skip to the next step in the overall set of steps.
    3. If started is true, let negated be false.
    4. Otherwise, if started is false and if bogus is false, let negated be true.
    5. Let started be true.
    A character in the range U+0030 DIGIT ZERO .. U+0039 DIGIT NINE

    Follow these substeps:

    1. If finished is true, skip to the next step in the overall set of steps.
    2. Multiply value by ten.
    3. Add the value of the digit, interpreted in base ten, to value.
    4. Let started be true.
    5. Let got number be true.
    A U+0020 SPACE character
    A U+002C COMMA character
    A U+003B SEMICOLON character

    Follow these substeps:

    1. If got number is false, return the numbers list and abort. This happens if an entry in the list has no digits, as in "1,2,x,4".
    2. If negated is true, then negate value.
    3. Append value to the numbers list.
    4. Jump to step 4 in the overall set of steps.
    A U+002E FULL STOP character

    Follow these substeps:

    1. If got number is true, let finished be true.
    2. If finished is true, skip to the next step in the overall set of steps.
    3. Let negated be false.
    Any other character

    Follow these substeps:

    1. If finished is true, skip to the next step in the overall set of steps.
    2. Let negated be false.
    3. Let bogus be true.
    4. If started is true, then return the numbers list, and abort. (The value in value is not appended to the list first; it is dropped.)
  14. Advance position to the next character in input, or to beyond the end of the string if there are no more characters.

  15. If position points to a character (and not to beyond the end of input), jump to the big Parser step above.

  16. If negated is true, then negate value.

  17. If got number is true, then append value to the numbers list.

  18. Return the numbers list and abort.

3.2.4 Dates and times

In the algorithms below, the number of days in month month of year year is: 31 if month is 1, 3, 5, 7, 8, 10, or 12; 30 if month is 4, 6, 9, or 11; 29 if month is 2 and year is a number divisible by 400, or if year is a number divisible by 4 but not by 100; and 28 otherwise. This takes into account leap years in the Gregorian calendar. [GREGORIAN]

3.2.4.1. Specific moments in time

A string is a valid datetime if it has four digits (representing the year), a literal hyphen, two digits (representing the month), a literal hyphen, two digits (representing the day), optionally some spaces, either a literal T or a space, optionally some more spaces, two digits (for the hour), a colon, two digits (the minutes), optionally the seconds (which, if included, must consist of another colon, two digits (the integer part of the seconds), and optionally a decimal point followed by one or more digits (for the fractional part of the seconds)), optionally some spaces, and finally either a literal Z (indicating the time zone is UTC), or, a plus sign or a minus sign followed by two digits, a colon, and two digits (for the sign, the hours and minutes of the timezone offset respectively); with the month-day combination being a valid date in the given year according to the Gregorian calendar, the hour values (h) being in the range 0 ≤ h ≤ 23, the minute values (m) in the range 0 ≤ m ≤ 59, and the second value (s) being in the range 0 ≤ h < 60. [GREGORIAN]

The digits must be characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), the hyphens must be a U+002D HYPHEN-MINUS characters, the T must be a U+0054 LATIN CAPITAL LETTER T, the colons must be U+003A COLON characters, the decimal point must be a U+002E FULL STOP, the Z must be a U+005A LATIN CAPITAL LETTER Z, the plus sign must be a U+002B PLUS SIGN, and the minus U+002D (same as the hyphen).

The following are some examples of dates written as valid datetimes.

"0037-12-13 00:00 Z"
Midnight UTC on the birthday of Nero (the Roman Emperor).
"1979-10-14T12:00:00.001-04:00"
One millisecond after noon on October 14th 1979, in the time zone in use on the east coast of North America during daylight saving time.
"8592-01-01 T 02:09 +02:09"
Midnight UTC on the 1st of January, 8592. The time zone associated with that time is two hours and nine minutes ahead of UTC.

Several things are notable about these dates:

Conformance checkers can use the algorithm below to determine if a datetime is a valid datetime or not.

To parse a string as a datetime value, a user agent must apply the following algorithm to the string. This will either return a time in UTC, with associated timezone information for round tripping or display purposes, or nothing, indicating the value is not a valid datetime. If at any point the algorithm says that it "fails", this means that it returns nothing.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly four characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the year.

  4. If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.

  5. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the month.

  6. If month is not a number in the range 1 ≤ month ≤ 12, then fail.
  7. Let maxday be the number of days in month month of year year.

  8. If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.

  9. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the day.

  10. If day is not a number in the range 1 ≤ month ≤ maxday, then fail.

  11. Collect a sequence of characters that are either U+0054 LATIN CAPITAL LETTER T characters or space characters. If the collected sequence is zero characters long, or if it contains more than one U+0054 LATIN CAPITAL LETTER T character, then fail.

  12. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the hour.

  13. If hour is not a number in the range 0 ≤ hour ≤ 23, then fail.
  14. If position is beyond the end of input or if the character at position is not a U+003A COLON character, then fail. Otherwise, move position forwards one character.

  15. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the minute.

  16. If minute is not a number in the range 0 ≤ minute ≤ 59, then fail.
  17. Let second be a string with the value "0".

  18. If position is beyond the end of input, then fail.

  19. If the character at position is a U+003A COLON, then:

    1. Advance position to the next character in input.

    2. If position is beyond the end of input, or at the last character in input, or if the next two characters in input starting at position are not two characters both in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), then fail.

    3. Collect a sequence of characters that are either characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9) or U+002E FULL STOP characters. If the collected sequence has more than one U+002E FULL STOP characters, or if the last character in the sequence is a U+002E FULL STOP character, then fail. Otherwise, let the collected string be second instead of its previous value.

  20. Interpret second as a base-ten number (possibly with a fractional part). Let that number be second instead of the string version.

  21. If second is not a number in the range 0 ≤ hour < 60, then fail. (The values 60 and 61 are not allowed: leap seconds cannot be represented by datetime values.)
  22. If position is beyond the end of input, then fail.

  23. Skip whitespace.

  24. If the character at position is a U+005A LATIN CAPITAL LETTER Z, then:

    1. Let timezonehours be 0.

    2. Let timezoneminutes be 0.

    3. Advance position to the next character in input.

  25. Otherwise, if the character at position is either a U+002B PLUS SIGN ("+") or a U+002D HYPHEN-MINUS ("-"), then:

    1. If the character at position is a U+002B PLUS SIGN ("+"), let sign be "positive". Otherwise, it's a U+002D HYPHEN-MINUS ("-"); let sign be "negative".

    2. Advance position to the next character in input.

    3. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the timezonehours.

    4. If timezonehours is not a number in the range 0 ≤ timezonehours ≤ 23, then fail.
    5. If sign is "negative", then negate timezonehours.
    6. If position is beyond the end of input or if the character at position is not a U+003A COLON character, then fail. Otherwise, move position forwards one character.

    7. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the timezoneminutes.

    8. If timezoneminutes is not a number in the range 0 ≤ timezoneminutes ≤ 59, then fail.
    9. If sign is "negative", then negate timezoneminutes.
  26. If position is not beyond the end of input, then fail.

  27. Let time be the moment in time at year year, month month, day day, hours hour, minute minute, second second, subtracting timezonehours hours and timezoneminutes minutes. That moment in time is a moment in the UTC timezone.

  28. Let timezone be timezonehours hours and timezoneminutes minutes from UTC.

  29. Return time and timezone.

3.2.4.2. Vaguer moments in time

This section defines date or time strings. There are two kinds, date or time strings in content, and date or time strings in attributes. The only difference is in the handling of whitespace characters.

To parse a date or time string, user agents must use the following algorithm. A date or time string is a valid date or time string if the following algorithm, when run on the string, doesn't say the string is invalid.

The algorithm may return nothing (in which case the string will be invalid), or it may return a date, a time, a date and a time, or a date and a time and a timezone. Even if the algorithm returns one or more values, the string can still be invalid.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let results be the collection of results that are to be returned (one or more of a date, a time, and a timezone), initially empty. If the algorithm aborts at any point, then whatever is currently in results must be returned as the result of the algorithm.

  4. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

  5. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

  6. Let the sequence of characters collected in the last step be s.

  7. If position is past the end of input, the string is invalid; abort these steps.

  8. If the character at position is not a U+003A COLON character, then:

    1. If the character at position is not a U+002D HYPHEN-MINUS ("-") character either, then the string is invalid, abort these steps.

    2. If the sequence s is not exactly four digits long, then the string is invalid. (This does not stop the algorithm, however.)

    3. Interpret the sequence of characters collected in step 5 as a base-ten integer, and let that number be year.

    4. Advance position past the U+002D HYPHEN-MINUS ("-") character.

    5. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

    6. If the sequence collected in the last step is not exactly two digits long, then the string is invalid.

    7. Interpret the sequence of characters collected two steps ago as a base-ten integer, and let that number be month.

    8. If month is not a number in the range 1 ≤ month ≤ 12, then the string is invalid, abort these steps.
    9. Let maxday be the number of days in month month of year year.

    10. If position is past the end of input, or if the character at position is not a U+002D HYPHEN-MINUS ("-") character, then the string is invalid, abort these steps. Otherwise, advance position to the next character.

    11. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

    12. If the sequence collected in the last step is not exactly two digits long, then the string is invalid.

    13. Interpret the sequence of characters collected two steps ago as a base-ten integer, and let that number be day.

    14. If day is not a number in the range 1 ≤ day ≤ maxday, then the string is invalid, abort these steps.

    15. Add the date represented by year, month, and day to the results.

    16. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

    17. If the character at position is a U+0054 LATIN CAPITAL LETTER T, then move position forwards one character.

    18. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

    19. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

    20. Let s be the sequence of characters collected in the last step.

  9. If s is not exactly two digits long, then the string is invalid.

  10. Interpret the sequence of characters collected two steps ago as a base-ten integer, and let that number be hour.

  11. If hour is not a number in the range 0 ≤ hour ≤ 23, then the string is invalid, abort these steps.

  12. If position is past the end of input, or if the character at position is not a U+003A COLON character, then the string is invalid, abort these steps. Otherwise, advance position to the next character.

  13. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

  14. If the sequence collected in the last step is not exactly two digits long, then the string is invalid.

  15. Interpret the sequence of characters collected two steps ago as a base-ten integer, and let that number be minute.

  16. If minute is not a number in the range 0 ≤ minute ≤ 59, then the string is invalid, abort these steps.

  17. Let second be 0. It may be changed to another value in the next step.

  18. If position is not past the end of input and the character at position is a U+003A COLON character, then:

    1. Collect a sequence of characters that are either characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9) or are U+002E FULL STOP. If the collected sequence is empty, or contains more than one U+002E FULL STOP character, then the string is invalid; abort these steps.

    2. If the first character in the sequence collected in the last step is not in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), then the string is invalid.

    3. Interpret the sequence of characters collected two steps ago as a base-ten number (possibly with a fractional part), and let that number be second.

    4. If second is not a number in the range 0 ≤ minute < 60, then the string is invalid, abort these steps.

  19. Add the time represented by hour, minute, and second to the results.

  20. If results has both a date and a time, then:

    1. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

    2. If position is past the end of input, then skip to the next step in the overall set of steps.

    3. Otherwise, if the character at position is a U+005A LATIN CAPITAL LETTER Z, then:

      1. Add the timezone corresponding to UTC (zero offset) to the results.

      2. Advance position to the next character in input.

      3. Skip to the next step in the overall set of steps.

    4. Otherwise, if the character at position is either a U+002B PLUS SIGN ("+") or a U+002D HYPHEN-MINUS ("-"), then:

      1. If the character at position is a U+002B PLUS SIGN ("+"), let sign be "positive". Otherwise, it's a U+002D HYPHEN-MINUS ("-"); let sign be "negative".

      2. Advance position to the next character in input.

      3. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then the string is invalid.

      4. Interpret the sequence collected in the last step as a base-ten number, and let that number be timezonehours.

      5. If timezonehours is not a number in the range 0 ≤ timezonehours ≤ 23, then the string is invalid; abort these steps.
      6. If sign is "negative", then negate timezonehours.
      7. If position is beyond the end of input or if the character at position is not a U+003A COLON character, then the string is invalid; abort these steps. Otherwise, move position forwards one character.

      8. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then the string is invalid.

      9. Interpret the sequence collected in the last step as a base-ten number, and let that number be timezoneminutes.

      10. If timezoneminutes is not a number in the range 0 ≤ timezoneminutes ≤ 59, then the string is invalid; abort these steps.
      11. Add the timezone corresponding to an offset of timezonehours hours and timezoneminutes minutes to the results.

      12. Skip to the next step in the overall set of steps.

    5. Otherwise, the string is invalid; abort these steps.

  21. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

  22. If position is not past the end of input, then the string is invalid.

  23. Abort these steps (the string is parsed).

3.2.5 Time offsets

valid time offset, rules for parsing time offsets, time offset serialization rules; in the format "5d4h3m2s1ms" or "3m 9.2s" or "00:00:00.00" or similar.

3.2.6 Tokens

A set of space-separated tokens is a set of zero or more words separated by one or more space characters, where words consist of any string of one or more characters, none of which are space characters.

A string containing a set of space-separated tokens may have leading or trailing space characters.

An unordered set of unique space-separated tokens is a set of space-separated tokens where none of the words are duplicated.

An ordered set of unique space-separated tokens is a set of space-separated tokens where none of the words are duplicated but where the order of the tokens is meaningful.

Sets of space-separated tokens sometimes have a defined set of allowed values. When a set of allowed values is defined, the tokens must all be from that list of allowed values; other values are non-conforming. If no such set of allowed values is provided, then all values are conforming.

When a user agent has to split a string on spaces, it must use the following algorithm:

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let tokens be a list of tokens, initially empty.

  4. Skip whitespace

  5. While position is not past the end of input:

    1. Collect a sequence of characters that are not space characters.

    2. Add the string collected in the previous step to tokens.

    3. Skip whitespace

  6. Return tokens.

When a user agent has to remove a token from a string, it must use the following algorithm:

  1. Let input be the string being modified.

  2. Let token be the token being removed. It will not contain any space characters.

  3. Let output be the output string, initially empty.

  4. Let position be a pointer into input, initially pointing at the start of the string.

  5. If position is beyond the end of input, set the string being modified to output, and abort these steps.

  6. If the character at position is a space character:

    1. Append the character at position to the end of output.

    2. Increment position so it points at the next character in input.

    3. Return to step 5 in the overall set of steps.

  7. Otherwise, the character at position is the first character of a token. Collect a sequence of characters that are not space characters, and let that be s.

  8. If s is exactly equal to token, then:

    1. Skip whitespace (in input).

    2. Remove any space characters currently at the end of output.

    3. If position is not past the end of input, and output is not the empty string, append a single U+0020 SPACE character at the end of output.

  9. Otherwise, append s to the end of output.

  10. Return to step 6 in the overall set of steps.

This causes any occurrences of the token to be removed from the string, and any spaces that were surrounding the token to be collapsed to a single space, except at the start and end of the string, where such spaces are removed.

3.2.7 Keywords and enumerated attributes

Some attributes are defined as taking one of a finite set of keywords. Such attributes are called enumerated attributes. The keywords are each defined to map to a particular state (several keywords might map to the same state, in which case some of the keywords are synonyms of each other; additionally, some of the keywords can be said to be non-conforming, and are only in the specification for historical reasons). In addition, two default states can be given. The first is the invalid value default, the second is the missing value default.

If an enumerated attribute is specified, the attribute's value must be one of the given keywords that are not said to be non-conforming, with no leading or trailing whitespace. The keyword may use any mix of uppercase and lowercase letters.

When the attribute is specified, if its value case-insensitively matches one of the given keywords then that keyword's state is the state that the attribute represents. If the attribute value matches none of the given keywords, but the attribute has an invalid value default, then the attribute represents that state. Otherwise, if the attribute value matches none of the keywords but there is a missing value default state defined, then that is the state represented by the attribute. Otherwise, there is no default, and invalid values must be ignored.

When the attribute is not specified, if there is a missing value default state defined, then that is the state represented by the (missing) attribute. Otherwise, the absence of the attribute means that there is no state represented.

The empty string can be one of the keywords in some cases. For example the contenteditable attribute has two states: true, matching the true keyword and the empty string, false, matching false and all other keywords (it's the invalid value default). It could further be thought of as having a third state inherit, which would be the default when the attribute is not specified at all (the missing value default), but for various reasons that isn't the way this specification actually defines it.

3.2.8 References

A valid hash-name reference to an element of type type is a string consisting of a U+0023 NUMBER SIGN (#) character followed by a string which exactly matches the value of the name attribute of an element in the document with type type.

The rules for parsing a hash-name reference to an element of type type are as follows:

  1. If the string being parsed does not contain a U+0023 NUMBER SIGN character, or if the first such character in the string is the last character in the string, then return null and abort these steps.

  2. Let s be the string from the character immediately after the first U+0023 NUMBER SIGN character in the string being parsed up to the end of that string.

  3. Return the first element of type type that has an id or name attribute whose value case-insensitively matches s.

3.2.9 URLs

This section will do the following:

3.3 Documents and document fragments

3.3.1 Semantics

Elements, attributes, and attribute values in HTML are defined (by this specification) to have certain meanings (semantics). For example, the ol element represents an ordered list, and the lang attribute represents the language of the content.

Authors must not use elements, attributes, and attribute values for purposes other than their appropriate intended semantic purpose.

For example, the following document is non-conforming, despite being syntactically correct:

<!DOCTYPE html>
<html lang="en-GB">
 <head> <title> Demonstration </title> </head>
 <body>
  <table>
   <tr> <td> My favourite animal is the cat. </td> </tr>
   <tr>
    <td>
     —<a href="http://example.org/~ernest/"><cite>Ernest</cite></a>,
     in an essay from 1992
    </td>
   </tr>
  </table>
 </body>
</html>

...because the data placed in the cells is clearly not tabular data (and the cite element mis-used). A corrected version of this document might be:

<!DOCTYPE html>
<html lang="en-GB">
 <head> <title> Demonstration </title> </head>
 <body>
  <blockquote>
   <p> My favourite animal is the cat. </p>
  </blockquote>
  <p>
   —<a href="http://example.org/~ernest/">Ernest</a>,
   in an essay from 1992
  </p>
 </body>
</html>

This next document fragment, intended to represent the heading of a corporate site, is similarly non-conforming because the second line is not intended to be a heading of a subsection, but merely a subheading or subtitle (a subordinate heading for the same section).

<body>
 <h1>ABC Company</h1>
 <h2>Leading the way in widget design since 1432</h2>
 ...

The header element should be used in these kinds of situations:

<body>
 <header>
  <h1>ABC Company</h1>
  <h2>Leading the way in widget design since 1432</h2>
 </header>
 ...

Through scripting and using other mechanisms, the values of attributes, text, and indeed the entire structure of the document may change dynamically while a user agent is processing it. The semantics of a document at an instant in time are those represented by the state of the document at that instant in time, and the semantics of a document can therefore change over time. User agents must update their presentation of the document as this occurs.

HTML has a progress element that describes a progress bar. If its "value" attribute is dynamically updated by a script, the UA would update the rendering to show the progress changing.

3.3.2 Structure

All the elements in this specification have a defined content model, which describes what nodes are allowed inside the elements, and thus what the structure of an HTML document or fragment must look like.

As noted in the conformance and terminology sections, for the purposes of determining if an element matches its content model or not, CDATASection nodes in the DOM are treated as equivalent to Text nodes, and entity reference nodes are treated as if they were expanded in place.

The space characters are always allowed between elements. User agents represent these characters between elements in the source markup as text nodes in the DOM. Empty text nodes and text nodes consisting of just sequences of those characters are considered inter-element whitespace.

Inter-element whitespace, comment nodes, and processing instruction nodes must be ignored when establishing whether an element matches its content model or not, and must be ignored when following algorithms that define document and element semantics.

An element A is said to be preceded or followed by a second element B if A and B have the same parent node and there are no other element nodes or text nodes (other than inter-element whitespace) between them.

Authors must not use elements in the HTML namespace anywhere except where they are explicitly allowed, as defined for each element, or as explicitly required by other specifications. For XML compound documents, these contexts could be inside elements from other namespaces, if those elements are defined as providing the relevant contexts.

The SVG specification defines the SVG foreignObject element as allowing foreign namespaces to be included, thus allowing compound documents to be created by inserting subdocument content under that element. This specification defines the XHTML html element as being allowed where subdocument fragments are allowed in a compound document. Together, these two definitions mean that placing an XHTML html element as a child of an SVG foreignObject element is conforming. [SVG]

The Atom specification defines the Atom content element, when its type attribute has the value xhtml, as requiring that it contains a single HTML div element. Thus, a div element is allowed in that context, even though this is not explicitly normatively stated by this specification. [ATOM]

In addition, elements in the HTML namespace may be orphan nodes (i.e. without a parent node).

For example, creating a td element and storing it in a global variable in a script is conforming, even though td elements are otherwise only supposed to be used inside tr elements.

var data = {
  name: "Banana",
  cell: document.createElement('td'), 
};

3.3.3 Kinds of content

Each element in HTML falls into zero or more categories that group elements with similar characteristics together. The following categories are used in this specification:

Some elements have unique requirements and do not fit into any particular category.

3.3.3.1. Metadata content

Metadata content is content that sets up the presentation or behavior of the rest of the content, or that sets up the relationship of the document with other documents, or that conveys other "out of band" information.

Elements from other namespaces whose semantics are primarily metadata-related (e.g. RDF) are also metadata content.

3.3.3.2. Flow content

Most elements that are used in the body of documents and applications are categorized as flow content.

As a general rule, elements whose content model allows any flow content should have either at least one descendant text node that is not inter-element whitespace, or at least one descendant element node that is embedded content. For the purposes of this requirement, del elements and their descendants must not be counted as contributing to the ancestors of the del element.

This requirement is not a hard requirement, however, as there are many cases where an element can be empty legitimately, for example when it is used as a placeholder which will later be filled in by a script, or when the element is part of a template and would on most pages be filled in but on some pages is not relevant.

3.3.3.3. Sectioning content

Sectioning content is content that defines the scope of headers, footers, and contact information.

Each sectioning content element potentially has a heading. See the section on headings and sections for further details.

3.3.3.4. Heading content

Heading content defines the header of a section (whether explicitly marked up using sectioning content elements, or implied by the heading content itself).

3.3.3.5. Phrasing content

Phrasing content is the text of the document, as well as elements that mark up that text at the intra-paragraph level. Runs of phrasing content form paragraphs.

All phrasing content is also flow content. Any content model that expects flow content also expects phrasing content.

As a general rule, elements whose content model allows any phrasing content should have either at least one descendant text node that is not inter-element whitespace, or at least one descendant element node that is embedded content. For the purposes of this requirement, nodes that are descendants of del elements must not be counted as contributing to the ancestors of the del element.

Most elements that are categorized as phrasing content can only contain elements that are themselves categorized as phrasing content, not any flow content.

Text nodes that are not inter-element whitespace are phrasing content.

3.3.3.6. Embedded content

Embedded content is content that imports another resource into the document, or content from another vocabulary that is inserted into the document.

All embedded content is also phrasing content (and flow content). Any content model that expects phrasing content (or flow content) also expects embedded content.

Elements that are from namespaces other than the HTML namespace and that convey content but not metadata, are embedded content for the purposes of the content models defined in this specification. (For example, MathML, or SVG.)

Some embedded content elements can have fallback content: content that is to be used when the external resource cannot be used (e.g. because it is of an unsupported format). The element definitions state what the fallback is, if any.

3.3.3.7. Interactive content

Parts of this section should eventually be moved to DOM3 Events.

Interactive content is content that is specifically intended for user interaction.

Certain elements in HTML can be activated, for instance a elements, button elements, or input elements when their type attribute is set to radio. Activation of those elements can happen in various (UA-defined) ways, for instance via the mouse or keyboard.

When activation is performed via some method other than clicking the pointing device, the default action of the event that triggers the activation must, instead of being activating the element directly, be to fire a click event on the same element.

The default action of this click event, or of the real click event if the element was activated by clicking a pointing device, must be to fire a further DOMActivate event at the same element, whose own default action is to go through all the elements the DOMActivate event bubbled through (starting at the target node and going towards the Document node), looking for an element with an activation behavior; the first element, in reverse tree order, to have one, must have its activation behavior executed.

The above doesn't happen for arbitrary synthetic events dispatched by author script. However, the click() method can be used to make it happen programmatically.

For certain form controls, this process is complicated further by changes that must happen around the click event. [WF2]

Most interactive elements have content models that disallow nesting interactive elements.

3.3.4 Transparent content models

Some elements are described as transparent; they have "transparent" as their content model. Some elements are described as semi-transparent; this means that part of their content model is "transparent" but that is not the only part of the content model that must be satisfied.

When a content model includes a part that is "transparent", those parts must not contain content that would not be conformant if all transparent and semi-transparent elements in the tree were replaced, in their parent element, by the children in the "transparent" part of their content model, retaining order.

When a transparent or semi-transparent element has no parent, then the part of its content model that is "transparent" must instead be treated as accepting any flow content.

3.3.5 Paragraphs

A paragraph is typically a block of text with one or more sentences that discuss a particular topic, as in typography, but can also be used for more general thematic grouping. For instance, an address is also a paragraph, as is a part of a form, a byline, or a stanza in a poem.

Paragraphs in flow content are defined relative to what the document looks like without the ins and del elements complicating matters. Let view be a view of the DOM that replaces all ins and del elements in the document with their contents. Then, in view, for each run of phrasing content uninterrupted by other types of content, in an element that accepts content other than phrasing content, let first be the first node of the run, and let last be the last node of the run. For each run, a paragraph exists in the original DOM from immediately before first to immediately after last. (Paragraphs can thus span across ins and del elements.)

A paragraph is also formed by p elements.

The p element can be used to wrap individual paragraphs when there would otherwise not be any content other than phrasing content to separate the paragraphs from each other.

In the following example, there are two paragraphs in a section. There is also a header, which contains phrasing content that is not a paragraph. Note how the comments and intra-element whitespace do not form paragraphs.

<section>
  <h1>Example of paragraphs</h1>
  This is the <em>first</em> paragraph in this example.
  <p>This is the second.</p>
  <!-- This is not a paragraph. -->
</section>

The following example takes that markup and puts ins and del elements around some of the markup to show that the text was changed (though in this case, the changes don't really make much sense, admittedly). Notice how this example has exactly the same paragraphs as the previous one, despite the ins and del elements.

<section>
  <ins><h1>Example of paragraphs</h1>
  This is the <em>first</em> paragraph in</ins> this example<del>.
  <p>This is the second.</p></del>
  <!-- This is not a paragraph. -->
</section>

3.4 Global attributes

The following attributes are common to and may be specified on all HTML elements (even those not defined in this specification):

Global attributes:
class
contenteditable
contextmenu
dir
draggable
id
irrelevant
lang
ref
registrationmark
style
tabindex
template
title

In addition, the following event handler content attributes may be specified on any HTML element:

Event handler content attributes:
onabort
onbeforeunload
onblur
onchange
onclick
oncontextmenu
ondblclick
ondrag
ondragend
ondragenter
ondragleave
ondragover
ondragstart
ondrop
onerror
onfocus
onkeydown
onkeypress
onkeyup
onload
onmessage
onmousedown
onmousemove
onmouseout
onmouseover
onmouseup
onmousewheel
onresize
onscroll
onselect
onstorage
onsubmit
onunload

Also, custom data attributes (e.g. data-foldername or data-msgid) can be specified on any HTML element, to store custom data specific to the page.

In HTML documents, the html element, and any other elements in the HTML namespace whose parent element is not in the HTML namespace, may have an xmlns attribute specified, if, and only if, it has the exact value "http://www.w3.org/1999/xhtml". This does not apply to XML documents.

In HTML, the xmlns attribute has absolutely no effect. It is basically a talisman. It is allowed merely to make migration to and from XHTML mildly easier. When parsed by an HTML parser, the attribute ends up in no namespace, not the "http://www.w3.org/2000/xmlns/" namespace like namespace declaration attributes in XML do.

In XML, an xmlns attribute is part of the namespace declaration mechanism, and an element cannot actually have an xmlns attribute in no namespace specified.

3.4.1 The id attribute

The id attribute represents its element's unique identifier. The value must be unique in the subtree within which the element finds itself and must contain at least one character. The value must not contain any space characters.

If the value is not the empty string, user agents must associate the element with the given value (exactly, including any space characters) for the purposes of ID matching within the subtree the element finds itself (e.g. for selectors in CSS or for the getElementById() method in the DOM).

Identifiers are opaque strings. Particular meanings should not be derived from the value of the id attribute.

This specification doesn't preclude an element having multiple IDs, if other mechanisms (e.g. DOM Core methods) can set an element's ID in a way that doesn't conflict with the id attribute.

The id DOM attribute must reflect the id content attribute.

3.4.2 The title attribute

The title attribute represents advisory information for the element, such as would be appropriate for a tooltip. On a link, this could be the title or a description of the target resource; on an image, it could be the image credit or a description of the image; on a paragraph, it could be a footnote or commentary on the text; on a citation, it could be further information about the source; and so forth. The value is text.

If this attribute is omitted from an element, then it implies that the title attribute of the nearest ancestor HTML element with a title attribute set is also relevant to this element. Setting the attribute overrides this, explicitly stating that the advisory information of any ancestors is not relevant to this element. Setting the attribute to the empty string indicates that the element has no advisory information.

If the title attribute's value contains U+000A LINE FEED (LF) characters, the content is split into multiple lines. Each U+000A LINE FEED (LF) character represents a line break.

Some elements, such as link and abbr, define additional semantics for the title attribute beyond the semantics described above.

The title DOM attribute must reflect the title content attribute.

3.4.3 The lang (HTML only) and xml:lang (XML only) attributes

The lang attribute specifies the primary language for the element's contents and for any of the element's attributes that contain text. Its value must be a valid RFC 3066 language code, or the empty string. [RFC3066]

The xml:lang attribute is defined in XML. [XML]

If these attributes are omitted from an element, then it implies that the language of this element is the same as the language of the parent element. Setting the attribute to the empty string indicates that the primary language is unknown.

The lang attribute may be used on elements of HTML documents. Authors must not use the lang attribute in XML documents.

The xml:lang attribute may be used on elements of XML documents. Authors must not use the xml:lang attribute in HTML documents.

To determine the language of a node, user agents must look at the nearest ancestor element (including the element itself if the node is an element) that has an xml:lang attribute set or is an HTML element and has a lang attribute set. That attribute specifies the language of the node.

If both the xml:lang attribute and the lang attribute are set on an element, user agents must use the xml:lang attribute, and the lang attribute must be ignored for the purposes of determining the element's language.

If no explicit language is given for the root element, then language information from a higher-level protocol (such as HTTP), if any, must be used as the final fallback language. In the absence of any language information, the default value is unknown (the empty string).

User agents may use the element's language to determine proper processing or rendering (e.g. in the selection of appropriate fonts or pronunciations, or for dictionary selection).

The lang DOM attribute must reflect the lang content attribute.

3.4.4 The xml:base attribute (XML only)

The xml:base attribute is defined in XML Base. [XMLBASE]

The xml:base attribute may be used on elements of XML documents. Authors must not use the xml:base attribute in HTML documents.

3.4.5 The dir attribute

The dir attribute specifies the element's text directionality. The attribute is an enumerated attribute with the keyword ltr mapping to the state ltr, and the keyword rtl mapping to the state rtl. The attribute has no defaults.

If the attribute has the state ltr, the element's directionality is left-to-right. If the attribute has the state rtl, the element's directionality is right-to-left. Otherwise, the element's directionality is the same as its parent element, or ltr if there is no parent element.

The processing of this attribute depends on the presentation layer. For example, CSS 2.1 defines a mapping from this attribute to the CSS 'direction' and 'unicode-bidi' properties, and defines rendering in terms of those properties.

The dir DOM attribute on an element must reflect the dir content attribute of that element, limited to only known values.

The dir DOM attribute on HTMLDocument objects must reflect the dir content attribute of the html element, if any, limited to only known values. If there is no such element, then the attribute must return the empty string and do nothing on setting.

3.4.6 The class attribute

Every HTML element may have a class attribute specified.

The attribute, if specified, must have a value that is an unordered set of unique space-separated tokens representing the various classes that the element belongs to.

The classes that an HTML element has assigned to it consists of all the classes returned when the value of the class attribute is split on spaces.

Assigning classes to an element affects class matching in selectors in CSS, the getElementsByClassName() method in the DOM, and other such features.

Authors may use any value in the class attribute, but are encouraged to use the values that describe the nature of the content, rather than values that describe the desired presentation of the content.

The className and classList DOM attributes must both reflect the class content attribute.

3.4.7 The irrelevant attribute

All elements may have the irrelevant content attribute set. The irrelevant attribute is a boolean attribute. When specified on an element, it indicates that the element is not yet, or is no longer, relevant. User agents should not render elements that have the irrelevant attribute specified.

In the following skeletal example, the attribute is used to hide the Web game's main screen until the user logs in:

  <h1>The Example Game</h1>
  <section id="login">
   <h2>Login</h2>
   <form>
    ...
    <!-- calls login() once the user's credentials have been checked -->
   </form>
   <script>
    function login() {
      // switch screens
      document.getElementById('login').irrelevant = true;
      document.getElementById('game').irrelevant = false;
    }
   </script>
  </section>
  <section id="game" irrelevant>
   ...
  </section>

The irrelevant attribute must not be used to hide content that could legitimately be shown in another presentation. For example, it is incorrect to use irrelevant to hide panels in a tabbed dialog, because the tabbed interface is merely a kind of overflow presentation — showing all the form controls in one big page with a scrollbar would be equivalent, and no less correct.

Elements in a section hidden by the irrelevant attribute are still active, e.g. scripts and form controls in such sections still render execute and submit respectively. Only their presentation to the user changes.

The irrelevant DOM attribute must reflect the content attribute of the same name.

3.4.8 The style attribute

All elements may have the style content attribute set. If specified, the attribute must contain only a list of zero or more semicolon-separated (;) CSS declarations. [CSS21]

The attribute, if specified, must be parsed and treated as the body (the part inside the curly brackets) of a declaration block in a rule whose selector matches just the element on which the attribute is set. For the purposes of the CSS cascade, the attribute must be considered to be a 'style' attribute at the author level.

Documents that use style attributes on any of their elements must still be comprehensible and usable if those attributes were removed.

In particular, using the style attribute to hide and show content, or to convey meaning that is otherwise not included in the document, is non-conforming.

The style DOM attribute must return a CSSStyleDeclaration whose value represents the declarations specified in the attribute, if present. Mutating the CSSStyleDeclaration object must create a style attribute on the element (if there isn't one already) and then change its value to be a value representing the serialized form of the CSSStyleDeclaration object. [CSSOM]

In the following example, the words that refer to colors are marked up using the span element and the style attribute to make those words show up in the relevant colors in visual media.

<p>My sweat suit is <span style="color: green; background:
transparent">green</span> and my eyes are <span style="color: blue;
background: transparent">blue</span>.</p>

3.4.9 Embedding custom non-visible data

A custom data attribute is an attribute whose name starts with the string "data-" and has at least one character after the hyphen.

Custom data attributes are intended to store custom data private to the page or application, for which there are no more appropriate attributes or elements.

Every HTML element may have any number of custom data attributes specified, with any value.

The dataset DOM attribute provides convenient accessors for all the data-* attributes on an element. On getting, the dataset DOM attribute must return a DOMStringMap object, associated with the following three algorithms, which expose these attributes on their element:

The algorithm for getting values from names
  1. Let name be the concatenation of the string data- and the name passed to the algorithm.
  2. If the element does not have an attribute with the name name, then the name has no corresponding value, abort.
  3. Otherwise, return the value of the attribute with the name name.
The algorithm for setting names to certain values
  1. Let name be the concatenation of the string data- and the name passed to the algorithm.
  2. Let value be the value passed to the algorithm.
  3. Set the value of the attribute with the name name, to the value value, replacing any previous value if the attribute already existed. If setAttribute() would have raised an exception when setting an attribute with the name name, then this must raise the same exception.
The algorithm for deleting names
  1. Let name be the concatenation of the string data- and the name passed to the algorithm.
  2. Remove the attribute with the name name, if such an attribute exists. Do nothing otherwise.

If a Web page wanted an element to represent a space ship, e.g. as part of a game, it would have to use the class attribute along with data-* attributes:

<div class="spaceship" data-id="92432"
     data-weapons="laser 2" data-shields="50%"
     data-x="30" data-y="10" data-z="90">
 <button class="fire"
         onclick="spaceships[this.parentNode.dataset.id].fire()">
  Fire
 </button>
</div>

Authors should carefully design such extensions so that when the attributes are ignored and any associated CSS dropped, the page is still usable.

User agents must not derive any implementation behavior from these attributes or values. Specifications intended for user agents must not define these attributes to have any meaningful values.

3.5 Interaction

3.5.1 Activation

The click() method must fire a click event at the element, whose default action is the firing of a further DOMActivate event at the same element, whose own default action is to go through all the elements the DOMActivate event bubbled through (starting at the target node and going towards the Document node), looking for an element with an activation behavior; the first element, in reverse tree order, to have one, must have its activation behavior executed.

3.5.2 Focus

When an element is focused, key events received by the document must be targeted at that element. There may be no element focused; when no element is focused, key events received by the document must be targetted at the body element.

User agents may track focus for each browsing context or Document individually, or may support only one focused elment per top-level browsing context — user agents should follow platform conventions in this regard.

Which element(s) within a top-level browsing context currently has focus must be independent of whether or not the top-level browsing context itself has the system focus.

3.5.2.1. Focus management

The focusing steps are as follows:

  1. If focusing the element will remove the focus from another element, then run the unfocusing steps for that element.

  2. Make the element the currently focused element in its top-level browsing context.

    Some elements, most notably area, can correspond to more than one distinct focusable area. If a particular area was indicated when the element was focused, then that is the area that must get focus; otherwise, e.g. when using the focus() method, the first such region in tree order is the one that must be focused.

  3. Fire a simple event that doesn't bubble called focus at the element.

User agents must run the focusing steps for an element whenever the user moves the focus to a focusable element.

The unfocusing steps are as follows:

  1. Unfocus the element.

  2. Fire a simple event that doesn't bubble called blur at the element.

User agents should run the unfocusing steps for an element whenever the user moves the focus away from any focusable element.


The focus() method, when invoked, must run the following algorithm:

  1. If the element is marked as locked for focus, then abort these steps.

  2. If the element is not focusable, then abort these steps.

  3. Mark the element as locked for focus.

  4. If the element is not already focused, run the focusing steps for the element.

  5. Unmark the element as locked for focus.

The blur() method, when invoked, should run the unfocusing steps for the element. User agents may selectively or uniformly ignore calls to this method for usability reasons.


The activeElement attribute must return the element in the document that is focused. If no element in the Document is focused, this must return the body element.

The hasFocus() method must return true if the document, one of its nested browsing contexts, or any element in the document or its browsing contexts currently has the system focus.

3.5.2.2. Sequential focus navigation

The tabindex content attribute specifies whether the element is focusable, whether it can be reached using sequential focus navigation, and the relative order of the element for the purposes of sequential focus navigation. The name "tab index" comes from the common use of the "tab" key to navigate through the focusable elements. The term "tabbing" refers to moving forward through the focusable elements that can be reached using sequential focus navigation.

The tabindex attribute, if specified, must have a value that is a valid integer.

If the attribute is specified, it must be parsed using the rules for parsing integers. The attribute's values have the following meanings:

If the attribute is omitted or parsing the value returns an error

The user agent should follow platform conventions to determine if the element is to be focusable and, if so, whether the element can be reached using sequential focus navigation, and if so, what its relative order should be.

If the value is a negative integer

The user agent must allow the element to be focused, but should not allow the element to be reached using sequential focus navigation.

If the value is a zero

The user agent must allow the element to be focused, should allow the element to be reached using sequential focus navigation, and should follow platform conventions to determine the element's relative order.

If the value is greater than zero

The user agent must allow the element to be focused, should allow the element to be reached using sequential focus navigation, and should place the element in the sequential focus navigation order so that it is:

An element is focusable if the tabindex attribute's definition above defines the element to be focusable and the element is being rendered.

When an element is focused, the element matches the CSS :focus pseudo-class and key events are dispatched on that element in response to keyboard input.

The tabIndex DOM attribute must reflect the value of the tabIndex content attribute. If the attribute is not present, or parsing its value returns an error, then the DOM attribute must return 0 for elements that are focusable and −1 for elements that are not focusable.

3.5.3 Scrolling elements into view

The scrollIntoView([top]) method, when called, must cause the element on which the method was called to have the attention of the user called to it.

In a speech browser, this could happen by having the current playback position move to the start of the given element.

In visual user agents, if the argument is present and has the value false, the user agent should scroll the element into view such that both the bottom and the top of the element are in the viewport, with the bottom of the element aligned with the bottom of the viewport. If it isn't possible to show the entire element in that way, or if the argument is omitted or is true, then the user agent should instead align the top of the element with the top of the viewport. Visual user agents should further scroll horizontally as necessary to bring the element to the attention of the user.

Non-visual user agents may ignore the argument, or may treat it in some media-specific manner most useful to the user.

3.6 The root element

3.6.1 The html element

Categories
None.
Contexts in which this element may be used:
As the root element of a document.
Wherever a subdocument fragment is allowed in a compound document.
Content model:
A head element followed by a body element.
Element-specific attributes:
manifest
DOM interface:
Uses HTMLElement.

The html element represents the root of an HTML document.

The manifest attribute gives the address of the document's application cache manifest, if there is one. If the attribute is present, the attribute's value must be a valid URI (or IRI).

The manifest attribute only has an effect during the early stages of document load. Changing the attribute dynamically thus has no effect (and thus, no DOM API is provided for this attribute).

Later base elements can't affect the resolving of relative URIs in manifest attributes, as the attributes are processed before those elements are seen.

3.7 Document metadata

3.7.1 The head element

Categories
None.
Contexts in which this element may be used:
As the first element in an html element.
Content model:
One or more elements of metadata content, of which exactly one is a title element.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The head element collects the document's metadata.

3.7.2 The title element

Categories
Metadata content.
Contexts in which this element may be used:
In a head element containing no other title elements.
Content model:
Text.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The title element represents the document's title or name. Authors should use titles that identify their documents even when they are used out of context, for example in a user's history or bookmarks, or in search results. The document's title is often different from its first header, since the first header does not have to stand alone when taken out of context.

There must be no more than one title element per document.

The title element must not contain any elements.

Here are some examples of appropriate titles, contrasted with the top-level headers that might be used on those same pages.

  <title>Introduction to The Mating Rituals of Bees</title>
    ...
  <h1>Introduction</h1>
  <p>This companion guide to the highly successful
  <cite>Introduction to Medieval Bee-Keeping</cite> book is...

The next page might be a part of the same site. Note how the title describes the subject matter unambiguously, while the first header assumes the reader knowns what the context is and therefore won't wonder if the dances are Salsa or Waltz:

  <title>Dances used during bee mating rituals</title>
    ...
  <h1>The Dances</h1>

The string to use as the document's title is given by the document.title DOM attribute. User agents should use the document's title when referring to the document in their user interface.

3.7.3 The base element

Categories
Metadata content.
Contexts in which this element may be used:
In a head element containing no other base elements.
Content model:
Empty.
Element-specific attributes:
href
target
DOM interface:
interface HTMLBaseElement : HTMLElement {
           attribute DOMString href;
           attribute DOMString target;
};

The base element allows authors to specify the document's base URI for the purposes of resolving relative URIs, and the name of the default browsing context for the purposes of following hyperlinks.

There must be no more than one base element per document.

A base element must have either an href attribute, a target attribute, or both.

The href content attribute, if specified, must contain a URI (or IRI).

A base element, if it has an href attribute, must come before any other elements in the tree that have attributes with URIs (except the html element and its manifest attribute).

User agents must use the value of the href attribute of the first base element that is both a child of the head element and has an href attribute, if there is such an element, as the document entity's base URI for the purposes of section 5.1.1 of RFC 3986 ("Establishing a Base URI": "Base URI Embedded in Content"). This base URI from RFC 3986 is referred to by the algorithm given in XML Base, which is a normative part of this specification. [RFC3986]

If the base URI given by this attribute is a relative URI, it must be resolved relative to the higher-level base URIs (i.e. the base URI from the encapsulating entity or the URI used to retrieve the entity) to obtain an absolute base URI. All xml:base attributes must be ignored when resolving relative URIs in this href attribute.

If there are multiple base elements with href attributes, all but the first are ignored.

The target attribute, if specified, must contain a valid browsing context name or keyword. User agents use this name when following hyperlinks.

A base element, if it has a target attribute, must come before any elements in the tree that represent hyperlinks.

The href and target DOM attributes must reflect the content attributes of the same name.

Categories
Metadata content.
Contexts in which this element may be used:
Where metadata content is expected.
In a noscript element that is a child of a head element.
Content model:
Empty.
Element-specific attributes:
href
rel
media
hreflang
type
sizes
Also, the title attribute has special semantics on this element.
DOM interface:
interface HTMLLinkElement : HTMLElement {
           attribute boolean disabled;
           attribute DOMString href;
           attribute DOMString rel;
  readonly attribute DOMTokenList relList;
           attribute DOMString media;
           attribute DOMString hreflang;
           attribute DOMString type;
           attribute DOMString sizes;
};

The LinkStyle interface must also be implemented by this element, the styling processing model defines how. [CSSOM]

The link element allows authors to link their document to other resources.

The destination of the link is given by the href attribute, which must be present and must contain a URI (or IRI). If the href attribute is absent, then the element does not define a link.

The type of link indicated (the relationship) is given by the value of the rel attribute, which must be present, and must have a value that is a set of space-separated tokens. The allowed values and their meanings are defined in a later section. If the rel attribute is absent, or if the value used is not allowed according to the definitions in this specification, then the element does not define a link.

Two categories of links can be created using the link element. Links to external resources are links to resources that are to be used to augment the current document, and hyperlink links are links to other documents. The link types section defines whether a particular link type is an external resource or a hyperlink. One element can create multiple links (of which some might be external resource links and some might be hyperlinks); exactly which and how many links are created depends on the keywords given in the rel attribute. User agents must process the links on a per-link basis, not a per-element basis.

The exact behavior for links to external resources depends on the exact relationship, as defined for the relevant link type. Some of the attributes control whether or not the external resource is to be applied (as defined below). For external resources that are represented in the DOM (for example, style sheets), the DOM representation must be made available even if the resource is not applied. (However, user agents may opt to only fetch such resources when they are needed, instead of pro-actively downloading all the external resources that are not applied.)

HTTP semantics must be followed when fetching external resources. (For example, redirects must be followed and 404 responses must cause the external resource to not be applied.)

Interactive user agents should provide users with a means to follow the hyperlinks created using the link element, somewhere within their user interface. The exact interface is not defined by this specification, but it should include the following information (obtained from the element's attributes, again as defined below), in some form or another (possibly simplified), for each hyperlink created with each link element in the document:

User agents may also include other information, such as the type of the resource (as given by the type attribute).

Hyperlinks created with the link element and its rel attribute apply to the whole page. This contrasts with the rel attribute of a and area elements, which indicates the type of a link whose context is given by the link's location within the document.

The media attribute says which media the resource applies to. The value must be a valid media query. [MQ]

If the link is a hyperlink then the media attribute is purely advisory, and describes for which media the document in question was designed.

However, if the link is an external resource link, then the media attribute is prescriptive. The user agent must apply the external resource to views while their state match the listed media, and must not apply them otherwise.

The default, if the media attribute is omitted, is all, meaning that by default links apply to all media.

The hreflang attribute on the link element has the same semantics as the hreflang attribute on hyperlink elements.

The type attribute gives the MIME type of the linked resource. It is purely advisory. The value must be a valid MIME type, optionally with parameters. [RFC2046]

For external resource links, user agents may use the type given in this attribute to decide whether or not to consider using the resource at all. If the UA does not support the given MIME type for the given link relationship, then the UA may opt not to download and apply the resource.

User agents must not consider the type attribute authoritative — upon fetching the resource, user agents must not use metadata included in the link to the resource to determine its type.

If the attribute is omitted, but the user agent would fetch the resource if the type was known and supported, then the user agent must fetch the resource and determine its type from its Content-Type metadata to determine if it supports (and can apply) that external resource. If no type metadata is specified, but the external resource link type has a default type defined, then the user agent must assume that the resource is of that type.

If a document contains four style sheet links labeled as follows:

<link rel="stylesheet" href="A" type="text/plain">
<link rel="stylesheet" href="B" type="text/css">
<link rel="stylesheet" href="C">

...then a compliant UA that supported only CSS style sheets would fetch the B and C files, and skip the A file (since text/plain is not the MIME type for CSS style sheets).

For files B and C, it would then check the actual types returned by the server. For those that are sent as text/css, it would apply the styles, but for those labeled as text/plain, or any other type, it would not.

If one the two files was returned without a Content-Type metadata, or with a syntactically incorrect type like Content-Type: "null", then the default type for stylesheet links would kick in. Since that default type is text/css, the style sheet would nonetheless be applied.

The title attribute gives the title of the link. With one exception, it is purely advisory. The value is text. The exception is for style sheet links, where the title attribute defines alternative style sheet sets.

The title attribute on link elements differs from the global title attribute of most other elements in that a link without a title does not inherit the title of the parent element: it merely has no title.

The sizes attribute is used with the icon link type. The attribute must not be specified on link elements that do not have a rel attribute that specifies the icon keyword.

Some versions of HTTP defined a Link: header, to be processed like a series of link elements. If supported, for the purposes of ordering links defined by HTTP headers must be assumed to come before any links in the document, in the order that they were given in the HTTP entity header. Relative URIs in these headers are resolved according to the rules given in HTTP, not relative to base URIs set by the document (e.g. using a base element or xml:base attributes). [RFC2616] [RFC2068]

The DOM attributes href, rel, media, hreflang, and type, and sizes each must reflect the respective content attributes of the same name.

The DOM attribute relList must reflect the rel content attribute.

The DOM attribute disabled only applies to style sheet links. When the link element defines a style sheet link, then the disabled attribute behaves as defined for the alternative style sheets DOM. For all other link elements it always return false and does nothing on setting.

3.7.5 The meta element

Categories
Metadata content.
Contexts in which this element may be used:
If the charset attribute is present, or if the element is in the Encoding declaration state: as the first element in a head element.
If the http-equiv attribute is present, and the element is not in the Encoding declaration state: in a head element.
If the http-equiv attribute is present, and the element is not in the Encoding declaration state: in a noscript element that is a child of a head element.
If the name attribute is present: where metadata content is expected.
Content model:
Empty.
Element-specific attributes:
name
http-equiv
content
charset (HTML only)
DOM interface:
interface HTMLMetaElement : HTMLElement {
           attribute DOMString content;
           attribute DOMString name;
           attribute DOMString httpEquiv;
};

The meta element represents various kinds of metadata that cannot be expressed using the title, base, link, style, and script elements.

The meta element can represent document-level metadata with the name attribute, pragma directives with the http-equiv attribute, and the file's character encoding declaration when an HTML document is serialized to string form (e.g. for transmission over the network or for disk storage) with the charset attribute.

Exactly one of the name, http-equiv, and charset attributes must be specified.

If either name or http-equiv is specified, then the content attribute must also be specified. Otherwise, it must be omitted.

The charset attribute specifies the character encoding used by the document. This is called a character encoding declaration.

The charset attribute may be specified in HTML documents only, it must not be used in XML documents. If the charset attribute is specified, the element must be the first element in the head element of the file.

The content attribute gives the value of the document metadata or pragma directive when the element is used for those purposes. The allowed values depend on the exact context, as described in subsequent sections of this specification.

If a meta element has a name attribute, it sets document metadata. Document metadata is expressed in terms of name/value pairs, the name attribute on the meta element giving the name, and the content attribute on the same element giving the value. The name specifies what aspect of metadata is being set; valid names and the meaning of their values are described in the following sections. If a meta element has no content attribute, then the value part of the metadata name/value pair is the empty string.

If a meta element has the http-equiv attribute specified, it must be either in a head element or in a noscript element that itself is in a head element. If a meta element does not have the http-equiv attribute specified, it must be in a head element.

The DOM attributes name and content must reflect the respective content attributes of the same name. The DOM attribute httpEquiv must reflect the content attribute http-equiv.

3.7.5.1. Standard metadata names

This specification defines a few names for the name attribute of the meta element.

application-name

The value must be a short free-form string that giving the name of the Web application that the page represents. If the page is not a Web application, the application-name metadata name must not be used. User agents may use the application name in UI in preference to the page's title, since the title might include status messages and the like relevant to the status of the page at a particular moment in time instead of just being the name of the application.

description

The value must be a free-form string that describes the page. The value must be appropriate for use in a directory of pages, e.g. in a search engine.

generator

The value must be a free-form string that identifies the software used to generate the document. This value must not be used on hand-authored pages.

3.7.5.2. Other metadata names

Extensions to the predefined set of metadata names may be registered in the WHATWG Wiki MetaExtensions page.

Anyone is free to edit the WHATWG Wiki MetaExtensions page at any time to add a type. These new names must be specified with the following information:

Keyword

The actual name being defined. The name should not be confusingly similar to any other defined name (e.g. differing only in case).

Brief description

A short description of what the metadata name's meaning is, including the format the value is required to be in.

Link to more details
A link to a more detailed description of the metadata name's semantics and requirements. It could be another page on the Wiki, or a link to an external page.
Synonyms

A list of other names that have exactly the same processing requirements. Authors should not use the names defined to be synonyms, they are only intended to allow user agents to support legacy content.

Status

One of the following:

Proposal
The name has not received wide peer review and approval. Someone has proposed it and is using it.
Accepted
The name has received wide peer review and approval. It has a specification that unambiguously defines how to handle pages that use the name, including when they use it in incorrect ways.
Unendorsed
The metadata name has received wide peer review and it has been found wanting. Existing pages are using this keyword, but new pages should avoid it. The "brief description" and "link to more details" entries will give details of what authors should use instead, if anything.

If a metadata name is added with the "proposal" status and found to be redundant with existing values, it should be removed and listed as a synonym for the existing value.

Conformance checkers must use the information given on the WHATWG Wiki MetaExtensions page to establish if a value not explicitly defined in this specification is allowed or not. When an author uses a new type not defined by either this specification or the Wiki page, conformance checkers should offer to add the value to the Wiki, with the details described above, with the "proposal" status.

This specification does not define how new values will get approved. It is expected that the Wiki will have a community that addresses this.

Metadata names whose values are to be URIs must not be proposed or accepted. Links must be represented using the link element, not the meta element.

3.7.5.3. Pragma directives

When the http-equiv attribute is specified on a meta element, the element is a pragma directive.

The http-equiv attribute is an enumerated attribute. The following table lists the keywords defined for this attribute. The states given in the first cell of the rows with keywords give the states to which those keywords map.

State Keywords
Encoding declaration Content-Type
Default style default-style
Refresh refresh

When a meta element is inserted into the document, if its http-equiv attribute is present and represents one of the above states, then the user agent must run the algorithm appropriate for that state, as described in the following list:

Encoding declaration state

The Encoding declaration state's user agent requirements are all handled by the parsing section of the specification. The state is just an alternative form of setting the charset attribute: it is a character encoding declaration.

For meta elements in the Encoding declaration state, the content attribute must have a value that is a case-insensitive match of a string that consists of the literal string "text/html;", optionally followed by any number of space characters, followed by the literal string "charset=", followed by the character encoding name of the character encoding declaration.

If the document contains a meta element in the Encoding declaration state then that element must be the first element in the document's head element, and the document must not contain a meta element with the charset attribute present.

The Encoding declaration state may be used in HTML documents only, elements in that state must not be used in XML documents.

Default style state
  1. ...
Refresh state
  1. If another meta element in the Refresh state has already been successfully processed (i.e. when it was inserted the user agent processed it and reached the last step of this list of steps), then abort these steps.

  2. If the meta element has no content attribute, or if that attribute's value is the empty string, then abort these steps.

  3. Let input be the value of the element's content attribute.

  4. Let position point at the first character of input.

  5. Skip whitespace.

  6. Collect a sequence of characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, and parse the resulting string using the rules for parsing non-negative integers. If the sequence of characters collected is the empty string, then no number will have been parsed; abort these steps. Otherwise, let time be the parsed number.

  7. Collect a sequence of characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE and U+002E FULL STOP ("."). Ignore any collected characters.

  8. Skip whitespace.

  9. Let url be the address of the current page.

  10. If the character in input pointed to by position is a U+003B SEMICOLON (";"), then advance position to the next character. Otherwise, jump to the last step.

  11. Skip whitespace.

  12. If the character in input pointed to by position is one of U+0055 LATIN CAPITAL LETTER U or U+0075 LATIN SMALL LETTER U, then advance position to the next character. Otherwise, jump to the last step.

  13. If the character in input pointed to by position is one of U+0052 LATIN CAPITAL LETTER R or U+0072 LATIN SMALL LETTER R, then advance position to the next character. Otherwise, jump to the last step.

  14. If the character in input pointed to by position is one of U+004C LATIN CAPITAL LETTER L or U+006C LATIN SMALL LETTER L, then advance position to the next character. Otherwise, jump to the last step.

  15. Skip whitespace.

  16. If the character in input pointed to by position is a U+003D EQUALS SIGN ("="), then advance position to the next character. Otherwise, jump to the last step.

  17. Skip whitespace.

  18. Let url be equal to the substring of input from the character at position to the end of the string.

  19. Strip any trailing space characters from the end of url.

  20. Strip any U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), and U+000D CARRIAGE RETURN (CR) characters from url.

  21. Resolve the url value to an absolute URI using the base URI of the meta element.

  22. Perform one or more of the following steps:

    • Set a timer so that in time seconds, adjusted to take into account user or user agent preferences, if the user has not canceled the redirect, the user agent navigates the document's browsing context to url, with replacement enabled, and with the document's browsing context as the source browsing context.

    • Provide the user with an interface that, when selected, navigates a browsing context to url, with the document's browsing context as the source browsing context.

    • Do nothing.

    In addition, the user agent may, as with anything, inform the user of any and all aspects of its operation, including the state of any timers, the destinations of any timed redirects, and so forth.

For meta elements in the Refresh state, the content attribute must have a value consisting either of:

In the former case, the integer represents a number of seconds before the page is to be reloaded; in the latter case the integer represents a number of seconds before the page is to be replaced by the page at the given URI.

There must not be more than one meta element with any particular state in the document at a time.

3.7.5.4. Specifying the document's character encoding

A character encoding declaration is a mechanism by which the character encoding used to store or transmit a document is specified.

The following restrictions apply to character encoding declarations:

If the document does not start with a BOM, and if its encoding is not explicitly given by Content-Type metadata, then the character encoding used must be an ASCII-compatible character encoding, and, in addition, if that encoding isn't US-ASCII itself, then the encoding must be specified using a meta element with a charset attribute or a meta element in the Encoding declaration state.

If the document contains a meta element with a charset attribute or a meta element in the Encoding declaration state, then the character encoding used must be an ASCII-compatible character encoding.

An ASCII-compatible character encoding is one that is a superset of US-ASCII (specifically, ANSI_X3.4-1968) for bytes in the range 0x09 - 0x0D, 0x20, 0x21, 0x22, 0x26, 0x27, 0x2C - 0x3F, 0x41 - 0x5A, and 0x61 - 0x7A.

Authors should not use JIS_X0212-1990, x-JIS0208, and encodings based on EBCDIC. Authors should not use UTF-32. Authors must not use the CESU-8, UTF-7, BOCU-1 and SCSU encodings. [CESU8] [UTF7] [BOCU1] [SCSU]

Authors are encouraged to use UTF-8. Conformance checkers may advise against authors using legacy encodings.

In XHTML, the XML declaration should be used for inline character encoding information, if necessary.

3.7.6 The style element

Categories
Metadata content.
If the scoped attribute is present: flow content.
Contexts in which this element may be used:
If the scoped attribute is absent: where metadata content is expected.
If the scoped attribute is absent: in a noscript element that is a child of a head element.
If the scoped attribute is present: where flow content is expected, but before any sibling elements other than style elements and before any text nodes other than inter-element whitespace.
Content model:
Depends on the value of the type attribute.
Element-specific attributes:
media
type
scoped
Also, the title attribute has special semantics on this element.
DOM interface:
interface HTMLStyleElement : HTMLElement {
           attribute boolean disabled;
           attribute DOMString media;
           attribute DOMString type;
           attribute boolean scoped;
};

The LinkStyle interface must also be implemented by this element, the styling processing model defines how. [CSSOM]

The style element allows authors to embed style information in their documents. The style element is one of several inputs to the styling processing model.

If the type attribute is given, it must contain a valid MIME type, optionally with parameters, that designates a styling language. [RFC2046] If the attribute is absent, the type defaults to text/css. [RFC2138]

When examining types to determine if they support the language, user agents must not ignore unknown MIME parameters — types with unknown parameters must be assumed to be unsupported.

The media attribute says which media the styles apply to. The value must be a valid media query. [MQ] User agents must apply the styles to views while their state match the listed media, and must not apply them otherwise. [DOM3VIEWS]

The default, if the media attribute is omitted, is all, meaning that by default styles apply to all media.

The scoped attribute is a boolean attribute. If the attribute is present, then the user agent must apply the specified style information only to the style element's parent element (if any), and that element's child nodes. Otherwise, the specified styles must, if applied, be applied to the entire document.

The title attribute on style elements defines alternative style sheet sets. If the style element has no title attribute, then it has no title; the title attribute of ancestors does not apply to the style element.

The title attribute on style elements, like the title attribute on link elements, differs from the global title attribute in that a style block without a title does not inherit the title of the parent element: it merely has no title.

All descendant elements must be processed, according to their semantics, before the style element itself is evaluated. For styling languages that consist of pure text, user agents must evaluate style elements by passing the concatenation of the contents of all the text nodes that are direct children of the style element (not any other nodes such as comments or elements), in tree order, to the style system. For XML-based styling languages, user agents must pass all the children nodes of the style element to the style system.

This specification does not specify a style system, but CSS is expected to be supported by most Web browsers. [CSS21]

The media, type and scoped DOM attributes must reflect the respective content attributes of the same name.

The DOM disabled attribute behaves as defined for the alternative style sheets DOM.

3.7.7 Styling

The link and style elements can provide styling information for the user agent to use when rendering the document. The DOM Styling specification specifies what styling information is to be used by the user agent and how it is to be used. [CSSOM]

The style and link elements implement the LinkStyle interface. [CSSOM]

For style elements, if the user agent does not support the specified styling language, then the sheet attribute of the element's LinkStyle interface must return null. Similarly, link elements that do not represent external resource links that contribute to the styling processing model (i.e. that do not have a stylesheet keyword in their rel attribute), and link elements whose specified resource has not yet been downloaded, or is not in a supported styling language, must have their LinkStyle interface's sheet attribute return null.

Otherwise, the LinkStyle interface's sheet attribute must return a StyleSheet object with the attributes implemented as follows: [CSSOM]

The content type (type DOM attribute)

The content type must be the same as the style's specified type. For style elements, this is the same as the type content attribute's value, or text/css if that is omitted. For link elements, this is the Content-Type metadata of the specified resource.

The location (href DOM attribute)

For link elements, the location must be the URI given by the element's href content attribute. For style elements, there is no location.

The intended destination media for style information (media DOM attribute)

The media must be the same as the value of the element's media content attribute.

The style sheet title (title DOM attribute)

The title must be the same as the value of the element's title content attribute. If the attribute is absent, then the style sheet does not have a title. The title is used for defining alternative style sheet sets.

The disabled DOM attribute on link and style elements must return false and do nothing on setting, if the sheet attribute of their LinkStyle interface is null. Otherwise, it must return the value of the StyleSheet interface's disabled attribute on getting, and forward the new value to that same attribute on setting.

3.8 Sections

Some elements, for example address elements, are scoped to their nearest ancestor sectioning content. For such elements x, the elements that apply to a sectioning content element e are all the x elements whose nearest sectioning content ancestor is e.

3.8.1 The body element

Categories
Sectioning content.
Contexts in which this element may be used:
As the second element in an html element.
Content model:
Flow content.
Element-specific attributes:
None.
DOM interface:
interface HTMLBodyElement : HTMLElement {};

The body element represents the main content of the document.

In conforming documents, there is only one body element. The document.body DOM attribute provides scripts with easy access to a document's body element.

Some DOM operations (for example, parts of the drag and drop model) are defined in terms of "the body element". This refers to a particular element in the DOM, as per the definition of the term, and not any arbitrary body element.

3.8.2 The section element

Categories
Flow content.
Sectioning content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The section element represents a generic document or application section. A section, in this context, is a thematic grouping of content, typically with a header, possibly with a footer.

Examples of sections would be chapters, the various tabbed pages in a tabbed dialog box, or the numbered sections of a thesis. A Web site's home page could be split into sections for an introduction, news items, contact information.

3.8.3 The nav element

Categories
Flow content.
Sectioning content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The nav element represents a section of a page that links to other pages or to parts within the page: a section with navigation links. Not all groups of links on a page need to be in a nav element — only sections that consist of primary navigation blocks are appropriate for the nav element. In particular, it is common for footers to have a list of links to various key parts of a site, but the footer element is more appropriate in such cases.

In the following example, the page has several places where links are present, but only one of those places is considered a navigation section.

<body>
 <header>
  <h1>Wake up sheeple!</h1>
  <p><a href="news.html">News</a> -
     <a href="blog.html">Blog</a> -
     <a href="forums.html">Forums</a></p>
 </header>
 <nav>
  <h1>Navigation</h1>
  <ul>
   <li><a href="articles.html">Index of all articles</a><li>
   <li><a href="today.html">Things sheeple need to wake up for today</a><li>
   <li><a href="successes.html">Sheeple we have managed to wake</a><li>
  </ul>
 </nav>
 <article>
  <p>...page content would be here...</p>
 </article>
 <footer>
  <p>Copyright © 2006 The Example Company</p>
  <p><a href="about.html">About</a> -
     <a href="policy.html">Privacy Policy</a> -
     <a href="contact.html">Contact Us</a></p>
 </footer>
</body>

3.8.4 The article element

Categories
Flow content.
Sectioning content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The article element represents a section of a page that consists of a composition that forms an independent part of a document, page, or site. This could be a forum post, a magazine or newspaper article, a Web log entry, a user-submitted comment, or any other independent item of content.

An article element is "independent" in that its contents could stand alone, for example in syndication. However, the element is still associated with its ancestors; for instance, contact information that applies to a parent body element still covers the article as well.

When article elements are nested, the inner article elements represent articles that are in principle related to the contents of the outer article. For instance, a Web log entry on a site that accepts user-submitted comments could represent the comments as article elements nested within the article element for the Web log entry.

Author information associated with an article element (q.v. the address element) does not apply to nested article elements.

3.8.5 The aside element

Categories
Flow content.
Sectioning content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The aside element represents a section of a page that consists of content that is tangentially related to the content around the aside element, and which could be considered separate from that content. Such sections are often represented as sidebars in printed typography.

The following example shows how an aside is used to mark up background material on Switzerland in a much longer news story on Europe.

<aside>
 <h1>Switzerland</h1>
 <p>Switzerland, a land-locked country in the middle of geographic
 Europe, has not joined the geopolitical European Union, though it is
 a signatory to a number of European treaties.</p>
</aside>

The following example shows how an aside is used to mark up a pull quote in a longer article.

...

<p>He later joined a large company, continuing on the same work.
<q>I love my job. People ask me what I do for fun when I'm not at
work. But I'm paid to do my hobby, so I never know what to
answer. Some people wonder what they would do if they didn't have to
work... but I know what I would do, because I was unemployed for a
year, and I filled that time doing exactly what I do
now.</q></p>

<aside>
 <q> People ask me what I do for fun when I'm not at work. But I'm
 paid to do my hobby, so I never know what to answer. </q>
</aside>

<p>Of course his work — or should that be hobby? —
isn't his only passion. He also enjoys other pleasures.</p>

...

3.8.6 The h1, h2, h3, h4, h5, and h6 elements

Categories
Flow content.
Heading content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

These elements define headers for their sections.

The semantics and meaning of these elements are defined in the section on headings and sections.

These elements have a rank given by the number in their name. The h1 element is said to have the highest rank, the h6 element has the lowest rank, and two elements with the same name have equal rank.

3.8.7 The header element

Categories
Flow content.
Heading content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content, including at least one descendant that is heading content, but no sectioning content descendants, no header element descendants, and no footer element descendants.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The header element represents the header of a section. The element is typically used to group a set of h1h6 elements to mark up a page's title with its subtitle or tagline. However, header elements may contain more than just the section's headings and subheadings — for example it would be reasonable for the header to include version history information.

For the purposes of document summaries, outlines, and the like, header elements are equivalent to the highest ranked h1h6 element descendant of the header element (the first such element if there are multiple elements with that rank).

Other heading elements in the header element indicate subheadings or subtitles.

The rank of a header element is the same as for an h1 element (the highest rank).

The section on headings and sections defines how header elements are assigned to individual sections.

Here are some examples of valid headers. In each case, the emphasised text represents the text that would be used as the header in an application extracting header data and ignoring subheadings.

<header>
 <h1>The reality dysfunction</h1>
 <h2>Space is not the only void</h2>
</header>
<header>
 <h1>Dr. Strangelove</h1>
 <h2>Or: How I Learned to Stop Worrying and Love the Bomb</h2>
</header>
<header>
 <p>Welcome to...</p>
 <h1>Voidwars!</h1>
</header>
<header>
 <h1>Scalable Vector Graphics (SVG) 1.2</h1>
 <h2>W3C Working Draft 27 October 2004</h2>
 <dl>
  <dt>This version:</dt>
  <dd><a href="http://www.w3.org/TR/2004/WD-SVG12-20041027/">http://www.w3.org/TR/2004/WD-SVG12-20041027/</a></dd>
  <dt>Previous version:</dt>
  <dd><a href="http://www.w3.org/TR/2004/WD-SVG12-20040510/">http://www.w3.org/TR/2004/WD-SVG12-20040510/</a></dd>
  <dt>Latest version of SVG 1.2:</dt>
  <dd><a href="http://www.w3.org/TR/SVG12/">http://www.w3.org/TR/SVG12/</a></dd>
  <dt>Latest SVG Recommendation:</dt>
  <dd><a href="http://www.w3.org/TR/SVG/">http://www.w3.org/TR/SVG/</a></dd>
  <dt>Editor:</dt>
  <dd>Dean Jackson, W3C, <a href="mailto:dean@w3.org">dean@w3.org</a></dd>
  <dt>Authors:</dt>
  <dd>See <a href="#authors">Author List</a></dd>
 </dl>
 <p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notic ...
</header>
Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content, but with no heading content descendants, no sectioning content descendants, and no footer element descendants.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The footer element represents the footer for the section it applies to. A footer typically contains information about its section such as who wrote it, links to related documents, copyright data, and the like.

Contact information for the section given in a footer should be marked up using the address element.

Footers don't necessarily have to appear at the end of a section, though they usually do.

Here is a page with two footers, one at the top and one at the bottom, with the same content:

<body>
 <footer><a href="../">Back to index...</a></footer>
 <h1>Lorem ipsum</h1>
 <p>A dolor sit amet, consectetur adipisicing elit, sed do eiusmod
 tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim
 veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex
 ea commodo consequat. Duis aute irure dolor in reprehenderit in
 voluptate velit esse cillum dolore eu fugiat nulla
 pariatur. Excepteur sint occaecat cupidatat non proident, sunt in
 culpa qui officia deserunt mollit anim id est laborum.</p>
 <footer><a href="../">Back to index...</a></footer>
</body>

3.8.9 The address element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content, but with no heading content descendants, no sectioning content descendants, no footer element descendants, and no address element descendants.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The address element represents the contact information for the section it applies to. If it applies to the body element, then it instead applies to the document as a whole.

For example, a page at the W3C Web site related to HTML might include the following contact information:

<ADDRESS>
 <A href="../People/Raggett/">Dave Raggett</A>, 
 <A href="../People/Arnaud/">Arnaud Le Hors</A>, 
 contact persons for the <A href="Activity">W3C HTML Activity</A>
</ADDRESS>

The address element must not be used to represent arbitrary addresses (e.g. postal addresses), unless those addresses are contact information for the section. (The p element is the appropriate element for marking up such addresses.)

The address element must not contain information other than contact information.

For example, the following is non-conforming use of the address element:

<ADDRESS>Last Modified: 1999/12/24 23:37:50</ADDRESS>

Typically, the address element would be included with other information in a footer element.

To determine the contact information for a sectioning content element (such as a document's body element, which would give the contact information for the page), UAs must collect all the address elements that apply to that sectioning content element and its ancestor sectioning content elements. The contact information is the collection of all the information given by those elements.

Contact information for one sectioning content element, e.g. an aside element, does not apply to its ancestor elements, e.g. the page's body.

3.8.10 Headings and sections

The h1h6 elements and the header element are headings.

The first element of heading content in an element of sectioning content gives the header for that section. Subsequent headers of equal or higher rank start new (implied) sections, headers of lower rank start subsections that are part of the previous one.

Sectioning content elements are always considered subsections of their nearest ancestor element of sectioning content, regardless of what implied sections other headings may have created.

Certain elements are said to be sectioning roots, including blockquote and td elements. These elements can have their own outlines, but the sections and headers inside these elements do not contribute to the outlines of their ancestors.

For the following fragment:

<body>
 <h1>Foo</h1>
 <h2>Bar</h2>
 <blockquote>
  <h3>Bla</h3>
 </blockquote>
 <p>Baz</p>
 <h2>Quux</h2>
 <section>
  <h3>Thud</h3>
 </section>
 <p>Grunt</p>
</body>

...the structure would be:

  1. Foo (heading of explicit body section, containing the "Grunt" paragraph)
    1. Bar (heading starting implied section, containing a block quote and the "Baz" paragraph)
    2. Quux (heading starting implied section)
    3. Thud (heading of explicit section section)

Notice how the section ends the earlier implicit section so that a later paragraph ("Grunt") is back at the top level.

Sections may contain headers of any rank, but authors are strongly encouraged to either use only h1 elements, or to use elements of the appropriate rank for the section's nesting level.

Authors are also encouraged to explicitly wrap sections in elements of sectioning content, instead of relying on the implicit sections generated by having multiple heading in one element of sectioning content.

For example, the following is correct:

<body>
 <h4>Apples</h4>
 <p>Apples are fruit.</p>
 <section>
  <h2>Taste</h2>
  <p>They taste lovely.</p>
  <h6>Sweet</h6>
  <p>Red apples are sweeter than green ones.</p>
  <h1>Color</h1>
  <p>Apples come in various colors.</p>
 </section>
</body>

However, the same document would be more clearly expressed as:

<body>
 <h1>Apples</h1>
 <p>Apples are fruit.</p>
 <section>
  <h2>Taste</h2>
  <p>They taste lovely.</p>
  <section>
   <h3>Sweet</h3>
   <p>Red apples are sweeter than green ones.</p>
  </section>
 </section>
 <section>
  <h2>Color</h2>
  <p>Apples come in various colors.</p>
 </section>
</body>

Both of the documents above are semantically identical and would produce the same outline in compliant user agents.

3.8.10.1. Creating an outline

This section defines an algorithm for creating an outline for a sectioning content element or a sectioning root element. It is defined in terms of a walk over the nodes of a DOM tree, in tree order, with each node being visited when it is entered and when it is exited during the walk.

The outline for a sectioning content element or a sectioning root element consists of a list of one or more potentially nested sections. Each section can have one heading associated with it. The algorithm for the outline also associates each node in the DOM tree with a particular section and potentially a heading. (The sections in the outline aren't section elements, though some may correspond to such elements — they are merely conceptual sections.)

The algorithm that must be followed during a walk of a DOM subtree rooted at a sectioning content element or a sectioning root element to determine that element's outline is as follows:

  1. Let current outlinee be null. (It holds the element whose outline is being created.)

  2. Let current section be null. (It holds a pointer to a section, so that elements in the DOM can all be associated with a section.)

  3. Create a stack to hold elements, which is used to handle nesting. Initialize this stack to empty.

  4. As you walk over the DOM in tree order, trigger the first relevant step below for each element as you enter and exit it.

    If the top of the stack is an element, and you are exiting that element

    The element being exited is a heading content element.

    Pop that element from the stack.

    If the top of the stack is a heading content element

    Do nothing.

    When entering a sectioning content element or a sectioning root element

    If current outlinee is not null, push current outlinee onto the stack.

    Let current outlinee be the element that is being entered.

    Let current section be a newly created section for the current outlinee element.

    Let there be a new outline for the new current outlinee, initialized with just the new current section as the only section in the outline.

    When exiting a sectioning content element, if the stack is not empty

    Pop the top element from the stack, and let the current outlinee be that element.

    Let current section be the last section in the outline of the current outlinee element.

    Append the outline of the sectioning content element being exited to the current section. (This does not change which section is the last section in the outline.)

    When exiting a sectioning root element, if the stack is not empty

    Run these steps:

    1. Pop the top element from the stack, and let the current outlinee be that element.

    2. Let current section be the last section in the outline of the current outlinee element.

    3. Loop: If current section has no child sections, stop these steps.

    4. Let current section be the last child section of the current current section.

    5. Go back to the substep labeled Loop.

    When exiting a sectioning content element or a sectioning root element

    The current outlinee is the element being exited.

    Let current section be the first section in the outline of the current outlinee element.

    Skip to the next step in the overall set of steps. (The walk is over.)

    If the current outlinee is null.

    Do nothing.

    When entering a heading content element

    If the current section has no heading, let the element being entered be the heading for the current section.

    Otherwise, if the element being entered has a rank equal to or greater than the heading of the current section, then create a new section and append it to the outline of the current outlinee element, so that this new section is the new last section of that outline. Let current section be that new section. Let the element being entered be the new heading for the current section.

    Otherwise, run these substeps:

    1. Let candidate section be current section.

    2. If the element being entered has a rank lower than the rank of the heading of the candidate section, then create a new section, and append it to candidate section. (This does not change which section is the last section in the outline.) Let current section be this new section. Let the element being entered be the new heading for the current section. Abort these substeps.

    3. Let candidate section be the section that contains the previous candidate section in the outline of current outlinee.

    4. Return to step 2.

    Push the element being entered onto the stack. (This causes the algorithm to skip any descendants of the element.)

    Otherwise

    Do nothing.

    In addition, whenever you exit a node, after doing the steps above, if current section is not null, associate the node with the section current section.

  5. If the current outlinee is null, then there was no sectioning content element or sectioning root element in the DOM. There is no outline. Abort these steps.

  6. Associate any nodes that were not associated a section in the steps above with current outlinee as their section.

  7. Associate all nodes with the heading of the section which which they are associated, if any.

  8. If current outlinee is the body element, then the outline created for that element is the outline of the entire document.

The tree of sections created by the algorithm above, or a proper subset thereof, must be used when generating document outlines, for example when generating tables of contents.

When creating an interactive table of contents, entries should jump the user to the relevant sectioning content element, if the section was created for a real element in the original document, or to the relevant heading content element, if the section in the tree was generated for a heading in the above process.

Selecting the first section of the document therefore always takes the user to the top of the document, regardless of where the first header in the body is to be found.

The following JavaScript function shows how the tree walk could be implemented. The root argument is the root of the tree to walk, and the enter and exit arguments are callbacks that are called with the nodes as they are entered and exited. [ECMA262]

function (root, enter, exit) {
  var node = root;
  start: do while (node) {
    enter(node);
    if (node.firstChild) {
      node = node.firstChild;
      continue start;
    }
    while (node) {
      exit(node);
      if (node.nextSibling) {
        node = node.nextSibling;
        continue start;
      }
      if (node == root)
        node = null;
      else
        node = node.parentNode;
    }
  }
}
3.8.10.2. Distinguishing site-wide headings from page headings

Given the outline of a document, but ignoring any sections created for nav and aside elements, and any of their descendants, if the only root of the tree is the body element's section, and it has only a single subsection which is created by an article element, then the heading of the body element should be assumed to be a site-wide heading, and the heading of the article element should be assumed to be the page's heading.

If a page starts with a heading that is common to the whole site, the document must be authored such that, in the document's outline, ignoring any sections created for nav and aside elements and any of their descendants, the tree has only one root section, the body element's section, its heading is the site-wide heading, the body element has just one subsection, that subsection is created by an article element, and that article's heading is the page heading.

If a page does not contain a site-wide heading, then the page must be authored such that, in the document's outline, ignoring any sections created for nav and aside elements and any of their descendants, either the body element has no subsections, or it has more than one subsection, or it has a single subsection but that subsection is not created by an article element, or there is more than one section at the root of the outline.

Conceptually, a site is thus a document with many articles — when those articles are split into many pages, the heading of the original single page becomes the heading of the site, repeated on every page.

3.9 Grouping content

3.9.1 The p element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The p element represents a paragraph.

The following examples are conforming HTML fragments:

<p>The little kitten gently seated himself on a piece of
carpet. Later in his life, this would be referred to as the time the
cat sat on the mat.</p>
<fieldset>
 <legend>Personal information</legend>
 <p>
   <label>Name: <input name="n"></label>
   <label><input name="anon" type="checkbox"> Hide from other users</label>
 </p>
 <p><label>Address: <textarea name="a"></textarea></label></p>
</fieldset>
<p>There was once an example from Femley,<br>
Whose markup was of dubious quality.<br>
The validator complained,<br>
So the author was pained,<br>
To move the error from the markup to the rhyming.</p>

The p element should not be used when a more specific element is more appropriate.

The following example is technically correct:

<section>
 <!-- ... -->
 <p>Last modified: 2001-04-23</p>
 <p>Author: fred@example.com</p>
</section>

However, it would be better marked-up as:

<section>
 <!-- ... -->
 <footer>Last modified: 2001-04-23</footer>
 <address>Author: fred@example.com</address>
</section>

Or:

<section>
 <!-- ... -->
 <footer>
  <p>Last modified: 2001-04-23</p>
  <address>Author: fred@example.com</address>
 </footer>
</section>

3.9.2 The hr element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Empty.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The hr element represents a paragraph-level thematic break, e.g. a scene change in a story, or a transition to another topic within a section of a reference book.

3.9.3 The br element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Empty.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The br element represents a line break.

br elements must be empty. Any content inside br elements must not be considered part of the surrounding text.

br elements must be used only for line breaks that are actually part of the content, as in poems or addresses.

The following example is correct usage of the br element:

<p>P. Sherman<br>
42 Wallaby Way<br>
Sydney</p>

br elements must not be used for separating thematic groups in a paragraph.

The following examples are non-conforming, as they abuse the br element:

<p><a ...>34 comments.</a><br>
<a ...>Add a comment.<a></p>
<p>Name: <input name="name"><br>
Address: <input name="address"></p>

Here are alternatives to the above, which are correct:

<p><a ...>34 comments.</a></p>
<p><a ...>Add a comment.<a></p>
<p>Name: <input name="name"></p>
<p>Address: <input name="address"></p>

If a paragraph consists of nothing but a single br element, it represents a placeholder blank line (e.g. as in a template). Such blank lines must not be used for presentation purposes.

3.9.4 The pre element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The pre element represents a block of preformatted text, in which structure is represented by typographic conventions rather than by elements.

In the HTML serialization, a leading newline character immediately following the pre element start tag is stripped.

Some examples of cases where the pre element could be used:

To represent a block of computer code, the pre element can be used with a code element; to represent a block of computer output the pre element can be used with a samp element. Similarly, the kbd element can be used within a pre element to indicate text that the user is to enter.

In the following snippet, a sample of computer code is presented.

<p>This is the <code>Panel</code> constructor:</p>
<pre><code>function Panel(element, canClose, closeHandler) {
  this.element = element;
  this.canClose = canClose;
  this.closeHandler = function () { if (closeHandler) closeHandler() };
}</code></pre>

In the following snippet, samp and kbd elements are mixed in the contents of a pre element to show a session of Zork I.

<pre><samp>You are in an open field west of a big white house with a boarded
front door.
There is a small mailbox here.

></samp> <kbd>open mailbox</kbd>

<samp>Opening the mailbox reveals:
A leaflet.

></samp></pre>

The following shows a contemporary poem that uses the pre element to preserve its unusual formatting, which forms an intrinsic part of the poem itself.

<pre>                maxling

it is with a          heart
               heavy

that i admit loss of a feline
        so           loved

a friend lost to the
        unknown
                                (night)

~cdr 11dec07</pre>

3.9.5 The dialog element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Zero or more pairs of one dt element followed by one dd element.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The dialog element represents a conversation.

Each part of the conversation must have an explicit talker (or speaker) given by a dt element, and a discourse (or quote) given by a dd element.

This example demonstrates this using an extract from Abbot and Costello's famous sketch, Who's on first:

<dialog>
 <dt> Costello
 <dd> Look, you gotta first baseman?
 <dt> Abbott
 <dd> Certainly.
 <dt> Costello
 <dd> Who's playing first?
 <dt> Abbott
 <dd> That's right.
 <dt> Costello
 <dd> When you pay off the first baseman every month, who gets the money?
 <dt> Abbott
 <dd> Every dollar of it. 
</dialog>

Text in a dt element in a dialog element is implicitly the source of the text given in the following dd element, and the contents of the dd element are implicitly a quote from that speaker. There is thus no need to include cite, q, or blockquote elements in this markup. Indeed, a q element inside a dd element in a conversation would actually imply the people talking were themselves quoting another work. See the cite, q, and blockquote elements for other ways to cite or quote.

3.9.6 The blockquote element

Categories
Flow content.
Sectioning root.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Element-specific attributes:
cite
DOM interface:
interface HTMLQuoteElement : HTMLElement {
           attribute DOMString cite;
};

The HTMLQuoteElement interface is also used by the q element.

The blockquote element represents a section that is quoted from another source.

Content inside a blockquote must be quoted from another source, whose URI, if it has one, should be cited in the cite attribute.

If the cite attribute is present, it must be a URI (or IRI). User agents should allow users to follow such citation links.

If a blockquote element is preceded or followed by a single paragraph that contains a single cite element and that is itself not preceded or followed by another blockquote element and does not itself have a q element descendant, then, the title of the work given by that cite element gives the source of the quotation contained in the blockquote element.

The cite DOM attribute must reflect the element's cite content attribute.

The best way to represent a conversation is not with the cite and blockquote elements, but with the dialog element.

3.9.7 The ol element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Zero or more li elements.
Element-specific attributes:
reversed
start
DOM interface:
interface HTMLOListElement : HTMLElement {
           attribute boolean reversed;
           attribute long start;
};

The ol element represents a list of items, where the items have been intentionally ordered, such that changing the order would change the meaning of the document.

The items of the list are the li element child nodes of the ol element, in tree order.

The reversed attribute is a boolean attribute. If present, it indicates that the list is a descending list (..., 3, 2, 1). If the attribute is omitted, the list is an ascending list (1, 2, 3, ...).

The start attribute, if present, must be a valid integer giving the ordinal value of the first list item.

If the start attribute is present, user agents must parse it as an integer, in order to determine the attribute's value. The default value, used if the attribute is missing or if the value cannot be converted to a number according to the referenced algorithm, is 1 if the element has no reversed attribute, and is the number of child li elements otherwise.

The first item in the list has the ordinal value given by the ol element's start attribute, unless that li element has a value attribute with a value that can be successfully parsed, in which case it has the ordinal value given by that value attribute.

Each subsequent item in the list has the ordinal value given by its value attribute, if it has one, or, if it doesn't, the ordinal value of the previous item, plus one if the reversed is absent, or minus one if it is present.

The reversed DOM attribute must reflect the value of the reversed content attribute.

The start DOM attribute must reflect the value of the start content attribute.

The following markup shows a list where the order matters, and where the ol element is therefore appropriate. Compare this list to the equivalent list in the ul section to see an example of the same items using the ul element.

<p>I have lived in the following countries (given in the order of when
I first lived there):</p>
<ol>
 <li>Switzerland
 <li>United Kingdom
 <li>United States
 <li>Norway
</ol>

Note how changing the order of the list changes the meaning of the document. In the following example, changing the relative order of the first two items has changed the birthplace of the author:

<p>I have lived in the following countries (given in the order of when
I first lived there):</p>
<ol>
 <li>United Kingdom
 <li>Switzerland
 <li>United States
 <li>Norway
</ol>

3.9.8 The ul element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Zero or more li elements.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The ul element represents a list of items, where the order of the items is not important — that is, where changing the order would not materially change the meaning of the document.

The items of the list are the li element child nodes of the ul element.

The following markup shows a list where the order does not matter, and where the ul element is therefore appropriate. Compare this list to the equivalent list in the ol section to see an example of the same items using the ol element.

<p>I have lived in the following countries:</p>
<ul>
 <li>Norway
 <li>Switzerland
 <li>United Kingdom
 <li>United States
</ul>

Note that changing the order of the list does not change the meaning of the document. The items in the snippet above are given in alphabetical order, but in the snippet below they are given in order of the size of their current account balance in 2007, without changing the meaning of the document whatsoever:

<p>I have lived in the following countries:</p>
<ul>
 <li>Switzerland
 <li>Norway
 <li>United Kingdom
 <li>United States
</ul>

3.9.9 The li element

Categories
None.
Contexts in which this element may be used:
Inside ol elements.
Inside ul elements.
Inside menu elements.
Content model:
When the element is a child of a menu element: phrasing content.
Otherwise: flow content.
Element-specific attributes:
If the element is a child of an ol element: value
If the element is not the child of an ol element: None.
DOM interface:
interface HTMLLIElement : HTMLElement {
           attribute long value;
};

The li element represents a list item. If its parent element is an ol, ul, or menu element, then the element is an item of the parent element's list, as defined for those elements. Otherwise, the list item has no defined list-related relationship to any other li element.

The value attribute, if present, must be a valid integer giving the ordinal value of the list item.

If the value attribute is present, user agents must parse it as an integer, in order to determine the attribute's value. If the attribute's value cannot be converted to a number, the attribute must be treated as if it was absent. The attribute has no default value.

The value attribute is processed relative to the element's parent ol element (q.v.), if there is one. If there is not, the attribute has no effect.

The value DOM attribute must reflect the value of the value content attribute.

The following example, the top ten movies are listed (in reverse order). Note the way the list is given a title by using a figure element and its legend.

<figure>
 <legend>The top 10 movies of all time</legend>
 <ol>
  <li value="10"><cite>Josie and the Pussycats</cite>, 2001</li>
  <li value="9"><cite lang="sh">Црна мачка, бели мачор</cite>, 1998</li>
  <li value="8"><cite>A Bugs Life</cite>, 1998</li>
  <li value="7"><cite>Toy Story</cite>, 1995</li>
  <li value="6"><cite>Monsters, Inc</cite>, 2001</li>
  <li value="5"><cite>Cars</cite>, 2006</li>
  <li value="4"><cite>Toy Story 2</cite>, 1999</li>
  <li value="3"><cite>Finding Nemo</cite>, 2003</li>
  <li value="2"><cite>The Incredibles</cite>, 2004</li>
  <li value="1"><cite>Ratatouille</cite>, 2007</li>
 </ol>
</figure>

The markup could also be written as follows, using the reversed attribute on the ol element:

<figure>
 <legend>The top 10 movies of all time</legend>
 <ol reversed>
  <li><cite>Josie and the Pussycats</cite>, 2001</li>
  <li><cite lang="sh">Црна мачка, бели мачор</cite>, 1998</li>
  <li><cite>A Bugs Life</cite>, 1998</li>
  <li><cite>Toy Story</cite>, 1995</li>
  <li><cite>Monsters, Inc</cite>, 2001</li>
  <li><cite>Cars</cite>, 2006</li>
  <li><cite>Toy Story 2</cite>, 1999</li>
  <li><cite>Finding Nemo</cite>, 2003</li>
  <li><cite>The Incredibles</cite>, 2004</li>
  <li><cite>Ratatouille</cite>, 2007</li>
 </ol>
</figure>

3.9.10 The dl element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Zero or more groups each consisting of one or more dt elements followed by one or mode dd elements.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The dl element introduces an association list consisting of zero or more name-value groups (a description list). Each group must consist of one or more names (dt elements) followed by one or more values (dd elements).

Name-value groups may be terms and definitions, metadata topics and values, or any other groups of name-value data.

The values within a group are alternatives; multiple paragraphs forming part of the same value must all be given within the same dd element.

The order of the list of groups, and of the names and values within each group, may be significant.

If a dl element is empty, it contains no groups.

If a dl element contains non-whitespace text nodes, or elements other than dt and dd, then those elements or text nodes do not form part of any groups in that dl.

If a dl element contains only dt elements, then it consists of one group with names but no values.

If a dl element contains only dd elements, then it consists of one group with values but no names.

If a dl element starts with one or more dd elements, then the first group has no associated name.

If a dl element ends with one or more dt elements, then the last group has no associated value.

When a dl element doesn't match its content model, it is often due to accidentally using dd elements in the place of dt elements and vice versa. Conformance checkers can spot such mistakes and might be able to advise authors how to correctly use the markup.

In the following example, one entry ("Authors") is linked to two values ("John" and "Luke").

<dl>
 <dt> Authors
 <dd> John
 <dd> Luke
 <dt> Editor
 <dd> Frank
</dl>

In the following example, one definition is linked to two terms.

<dl>
 <dt lang="en-US"> <dfn>color</dfn> </dt>
 <dt lang="en-GB"> <dfn>colour</dfn> </dt>
 <dd> A sensation which (in humans) derives from the ability of
 the fine structure of the eye to distinguish three differently
 filtered analyses of a view. </dd>
</dl>

The following example illustrates the use of the dl element to mark up metadata of sorts. At the end of the example, one group has two metadata labels ("Authors" and "Editors") and two values ("Robert Rothman" and "Daniel Jackson").

<dl>
 <dt> Last modified time </dt>
 <dd> 2004-12-23T23:33Z </dd>
 <dt> Recommended update interval </dt>
 <dd> 60s </dd>
 <dt> Authors </dt>
 <dt> Editors </dt>
 <dd> Robert Rothman </dd>
 <dd> Daniel Jackson </dd>
</dl>

The following example shows the dl element used to give a set of instructions. The order of the instructions here is important (in the other examples, the order of the blocks was not important).

<p>Determine the victory points as follows (use the
first matching case):</p>
<dl>
 <dt> If you have exactly five gold coins </dt>
 <dd> You get five victory points </dd>
 <dt> If you have one or more gold coins, and you have one or more silver coins </dt>
 <dd> You get two victory points </dd>
 <dt> If you have one or more silver coins </dt>
 <dd> You get one victory point </dd>
 <dt> Otherwise </dt>
 <dd> You get no victory points </dd>
</dl>

The following snippet shows a dl element being used as a glossary. Note the use of dfn to indicate the word being defined.

<dl>
 <dt><dfn>Apartment</dfn>, n.</dt>
 <dd>An execution context grouping one or more threads with one or
 more COM objects.</dd>
 <dt><dfn>Flat</dfn>, n.</dt>
 <dd>A deflated tire.</dd>
 <dt><dfn>Home</dfn>, n.</dt>
 <dd>The user's login directory.</dd>
</dl>

The dl element is inappropriate for marking up dialogue, since dialogue is ordered (each speaker/line pair comes after the next). For an example of how to mark up dialogue, see the dialog element.

3.9.11 The dt element

Categories
None.
Contexts in which this element may be used:
Before dd or dt elements inside dl elements.
Before a dd element inside a dialog element.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The dt element represents the term, or name, part of a term-description group in a description list (dl element), and the talker, or speaker, part of a talker-discourse pair in a conversation (dialog element).

The dt element itself, when used in a dl element, does not indicate that its contents are a term being defined, but this can be indicated using the dfn element.

If the dt element is the child of a dialog element, and it further contains a time element, then that time element represents a timestamp for when the associated discourse (dd element) was said, and is not part of the name of the talker.

The following extract shows how an IM conversation log could be marked up.

<dialog>
 <dt> <time>14:22</time> egof
 <dd> I'm not that nerdy, I've only seen 30% of the star trek episodes
 <dt> <time>14:23</time> kaj
 <dd> if you know what percentage of the star trek episodes you have seen, you are inarguably nerdy
 <dt> <time>14:23</time> egof
 <dd> it's unarguably
 <dt> <time>14:24</time> kaj
 <dd> you are not helping your case
</dialog>

3.9.12 The dd element

Categories
None.
Contexts in which this element may be used:
After dt or dd elements inside dl elements.
After a dt element inside a dialog element.
Content model:
Flow content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The dd element represents the description, definition, or value, part of a term-description group in a description list (dl element), and the discourse, or quote, part in a conversation (dialog element).

3.10 Text-level semantics

3.10.1 The a element

Categories
Phrasing content.
Interactive content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content, but there must be no interactive content descendant.
Element-specific attributes:
href
target
ping
rel
media
hreflang
type
DOM interface:
[Stringifies=href] interface HTMLAnchorElement : HTMLElement {
           attribute DOMString href;
           attribute DOMString target;
           attribute DOMString ping;
           attribute DOMString rel;
  readonly attribute DOMTokenList relList;
           attribute DOMString media;
           attribute DOMString hreflang;
           attribute DOMString type;
};

The Command interface must also be implemented by this element.

If the a element has an href attribute, then it represents a hyperlink.

If the a element has no href attribute, then the element is a placeholder for where a link might otherwise have been placed, if it had been relevant.

The target, ping, rel, media, hreflang, and type attributes must be omitted if the href attribute is not present.

If a site uses a consistent navigation toolbar on every page, then the link that would normally link to the page itself could be marked up using an a element:

<nav>
 <ul>
  <li> <a href="/">Home</a> </li>
  <li> <a href="/news">News</a> </li>
  <li> <a>Examples</a> </li>
  <li> <a href="/legal">Legal</a> </li>
 </ul>
</nav>

Interactive user agents should allow users to follow hyperlinks created using the a element. The href, target and ping attributes decide how the link is followed. The rel, media, hreflang, and type attributes may be used to indicate to the user the likely nature of the target resource before the user follows the link.

The activation behavior of a elements that represent hyperlinks is to run the following steps:

  1. If the DOMActivate event in question is not trusted (i.e. a click() method call was the reason for the event being dispatched), and the a element's target attribute is ... then raise an INVALID_ACCESS_ERR exception and abort these steps.

  2. If the target of the DOMActivate event is an img element with an ismap attribute specified, then server-side image map processing must be performed, as follows:

    1. If the DOMActivate event was dispatched as the result of a real pointing-device-triggered click event on the img element, then let x be the distance in CSS pixels from the left edge of the image to the location of the click, and let y be the distance in CSS pixels from the top edge of the image to the location of the click. Otherwise, let x and y be zero.
    2. Let the hyperlink suffix be a U+003F QUESTION MARK character, the value of x expressed as a base-ten integer using ASCII digits (U+0030 DIGIT ZERO to U+0039 DIGIT NINE), a U+002C COMMA character, and the value of y expressed as a base-ten integer using ASCII digits.
  3. Finally, the user agent must follow the hyperlink defined by the a element. If the steps above defined a hyperlink suffix, then take that into account when following the hyperlink.

One way that a user agent can enable users to follow hyperlinks is by allowing a elements to be clicked, or focussed and activated by the keyboard. This will cause the aforementioned activation behavior to be invoked.

The DOM attributes href, ping, target, rel, media, hreflang, and type, must each reflect the respective content attributes of the same name.

The DOM attribute relList must reflect the rel content attribute.

3.10.2 The q element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
cite
DOM interface:
The q element uses the HTMLQuoteElement interface.

The q element represents some phrasing content quoted from another source.

Quotation punctuation (such as quotation marks), if any, must be placed inside the q element.

Content inside a q element must be quoted from another source, whose URI, if it has one, should be cited in the cite attribute.

If the cite attribute is present, it must be a URI (or IRI). User agents should allow users to follow such citation links.

If a q element is contained (directly or indirectly) in a paragraph that contains a single cite element and has no other q element descendants, then, the title of the work given by that cite element gives the source of the quotation contained in the q element.

Here is a simple example of the use of the q element:

<p>The man said <q>"Things that are impossible just take
longer"</q>. I disagreed with him.</p>

Here is an example with both an explicit citation link in the q element, and an explicit citation outside:

<p>The W3C page <cite>About W3C</cite> says the W3C's
mission is <q cite="http://www.w3.org/Consortium/">"To lead the
World Wide Web to its full potential by developing protocols and
guidelines that ensure long-term growth for the Web"</q>. I
disagree with this mission.</p>

In the following example, the quotation itself contains a quotation:

<p>In <cite>Example One</cite>, he writes <q>"The man
said <q>'Things that are impossible just take longer'</q>. I
disagreed with him"</q>. Well, I disagree even more!</p>

In the following example, there are no quotation marks:

<p>His best argument: <q>I disagree!</q></p>

3.10.3 The cite element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The cite element represents the title of a work (e.g. a book, a paper, an essay, a poem, a score, a song, a script, a film, a TV show, a game, a sculpture, a painting, a theatre production, a play, an opera, a musical, an exhibition, etc). This can be a work that is being quoted or referenced in detail (i.e. a citation), or it can just be a work that is mentioned in passing.

A person's name is not the title of a work — even if people call that person a piece of work — and the element must therefore not be used to mark up people's names. (In some cases, the b element might be appropriate for names; e.g. in a gossip article where the names of famous people are keywords rendered with a different style to draw attention to them. In other cases, if an element is really needed, the span element can be used.)

A ship is similarly not a work, and the element must not be used to mark up ship names (the i element can be used for that purpose).

This next example shows a typical use of the cite element:

<p>My favourite book is <cite>The Reality Dysfunction</cite> by
Peter F. Hamilton. My favourite comic is <cite>Pearls Before
Swine</cite> by Stephan Pastis. My favourite track is <cite>Jive
Samba</cite> by the Cannonball Adderley Sextet.</p>

This is correct usage:

<p>According to the Wikipedia article <cite>HTML</cite>, as it
stood in mid-February 2008, leaving attribute values unquoted is
unsafe. This is obviously an over-simplification.</p>

The following, however, is incorrect usage, as the cite element here is containing far more than the title of the work:

<!-- do not copy this example, it is an example of bad usage! -->
<p>According to <cite>the Wikipedia article on HTML</cite>, as it
stood in mid-February 2008, leaving attribute values unquoted is
unsafe. This is obviously an over-simplification.</p>

The cite element is obviously a key part of any citation in a bibliography, but it is only used to mark the title:

<p><cite>Universal Declaration of Human Rights</cite>, United Nations,
December 1948.  Adopted by General Assembly resolution 217 A (III).</p>

A citation is not a quote (for which the q element is appropriate).

This is incorrect usage, because cite is not for quotes:

<p><cite>This is wrong!</cite>, said Ian.</p>

This is also incorrect usage, because a person is not a work:

<p><q>This is still wrong!</q>, said <cite>Ian</cite>.</p>

The correct usage does not use a cite element:

<p><q>This is correct</q>, said Ian.</p>

As mentioned above, the b element might be relevant for marking names as being keywords in certain kinds of documents:

<p>And then <b>Ian</b> said <q>this might be right, in a
gossip column, maybe!</q>.</p>

The cite element can apply to blockquote and q elements in certain cases described in the definitions of those elements.

This next example shows the use of cite alongside blockquote:

<p>His next piece was the aptly named <cite>Sonnet 130</cite>:</p>
<blockquote>
  <p>My mistress' eyes are nothing like the sun,<br>
  Coral is far more red, than her lips red,
  ...

3.10.4 The em element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The em element represents stress emphasis of its contents.

The level of emphasis that a particular piece of content has is given by its number of ancestor em elements.

The placement of emphasis changes the meaning of the sentence. The element thus forms an integral part of the content. The precise way in which emphasis is used in this way depends on the language.

These examples show how changing the emphasis changes the meaning. First, a general statement of fact, with no emphasis:

<p>Cats are cute animals.</p>

By emphasizing the first word, the statement implies that the kind of animal under discussion is in question (maybe someone is asserting that dogs are cute):

<p><em>Cats</em> are cute animals.</p>

Moving the emphasis to the verb, one highlights that the truth of the entire sentence is in question (maybe someone is saying cats are not cute):

<p>Cats <em>are</em> cute animals.</p>

By moving it to the adjective, the exact nature of the cats is reasserted (maybe someone suggested cats were mean animals):

<p>Cats are <em>cute</em> animals.</p>

Similarly, if someone asserted that cats were vegetables, someone correcting this might emphasize the last word:

<p>Cats are cute <em>animals</em>.</p>

By emphasizing the entire sentence, it becomes clear that the speaker is fighting hard to get the point across. This kind of emphasis also typically affects the punctuation, hence the exclamation mark here.

<p><em>Cats are cute animals!</em></p>

Anger mixed with emphasizing the cuteness could lead to markup such as:

<p><em>Cats are <em>cute</em> animals!</em></p>

3.10.5 The strong element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The strong element represents strong importance for its contents.

The relative level of importance of a piece of content is given by its number of ancestor strong elements; each strong element increases the importance of its contents.

Changing the importance of a piece of text with the strong element does not change the meaning of the sentence.

Here is an example of a warning notice in a game, with the various parts marked up according to how important they are:

<p><strong>Warning.</strong> This dungeon is dangerous.
<strong>Avoid the ducks.</strong> Take any gold you find.
<strong><strong>Do not take any of the diamonds</strong>,
they are explosive and <strong>will destroy anything within
ten meters.</strong></strong> You have been warned.</p>

3.10.6 The small element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The small element represents small print (part of a document often describing legal restrictions, such as copyrights or other disadvantages), or other side comments.

The small element does not "de-emphasize" or lower the importance of text emphasised by the em element or marked as important with the strong element.

In this example the footer contains contact information and a copyright.

<footer>
 <address>
  For more details, contact
  <a href="mailto:js@example.com">John Smith</a>.
 </address>
 <p><small>© copyright 2038 Example Corp.</small></p>
</footer>

In this second example, the small element is used for a side comment.

<p>Example Corp today announced record profits for the
second quarter <small>(Full Disclosure: Foo News is a subsidiary of
Example Corp)</small>, leading to speculation about a third quarter
merger with Demo Group.</p>

In this last example, the small element is marked as being important small print.

<p><strong><small>Continued use of this service will result in a kiss.</small></strong></p>

3.10.7 The mark element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The mark element represents a run of text in one document marked or highlighted for reference purposes, due to its relevance in another context. When used in a quotation or other block of text referred to from the prose, it indicates a highlight that was not originally present but which has been added to bring the reader's attention to a part of the text that might not have been considered important by the original author when the block was originally written, but which is now under previously unexpected scrutiny. When used in the main prose of a document, it indicates a part of the document that has been highlighted due to its likely relevance to the user's current activity.

The rendering section will eventually suggest that user agents provide a way to let users jump between mark elements. Suggested rendering is a neon yellow background highlight, though UAs maybe should allow this to be toggled.

This example shows how the mark example can be used to bring attention to a particular part of a quotation:

<p lang="en-US">Consider the following quote:</p>
<blockquote lang="en-GB">
 <p>Look around and you will find, no-one's really
 <mark>colour</mark> blind.</p>
</blockquote>
<p lang="en-US">As we can tell from the <em>spelling</em> of the word,
the person writing this quote is clearly not American.</p>

Another example of the mark element is highlighting parts of a document that are matching some search string. If someone looked at a document, and the server knew that the user was searching for the word "kitten", then the server might return the document with one paragraph modified as follows:

<p>I also have some <mark>kitten</mark>s who are visiting me
these days. They're really cute. I think they like my garden! Maybe I
should adopt a <mark>kitten</mark>.</p>

In the following snippet, a paragraph of text refers to a specific part of a code fragment.

<p>The highlighted part below is where the error lies:</p>
<pre><code>var i: Integer;
begin
   i := <mark>1.1</mark>;
end.</code></pre>

This is another example showing the use of mark to highlight a part of quoted text that was originally not emphasised. In this example, common typographic conventions have led the author to explicitly style mark elements in quotes to render in italics.

<article>
 <style>
  blockquote mark, q mark {
    font: inherit; font-style: italic;
    text-decoration: none;
    background: transparent; color: inherit;
  }
  .bubble em {
    font: inherit; font-size: larger;
    text-decoration: underline;
  }
 </style>
 <h1>She knew</h1>
 <p>Did you notice the subtle joke in the joke on panel 4?</p>
 <blockquote>
  <p class="bubble">I didn't <em>want</em> to believe. <mark>Of course
  on some level I realized it was a known-plaintext attack.</mark> But I
  couldn't admit it until I saw for myself.</p>
 </blockquote>
 <p>(Emphasis mine.) I thought that was great. It's so pedantic, yet it
 explains everything neatly.</p>
</article>

Note, incidentally, the distinction between the em element in this example, which is part of the original text being quoted, and the mark element, which is highlighting a part for comment.

The following example shows the difference between denoting the importance of a span of text (strong) as opposed to denoting the relevance of a span of text (mark). It is an extract from a textbook, where the extract has had the parts relevant to the exam highlighted. The safety warnings, important though they may be, are apparently not relevant to the exam.

<h3>Wormhole Physics Introduction</h3>

<p><mark>A wormhole in normal conditions can be held open for a
maximum of just under 39 minutes.</mark> Conditions that can increase
the time include a powerful energy source coupled to one or both of
the gates connecting the wormhole, and a large gravity well (such as a
black hole).</p>

<p><mark>Momentum is preserved across the wormhole. Electromagnetic
radiation can travel in both directions through a wormhole,
but matter cannot.</mark></p>

<p>When a wormhole is created, a vortex normally forms.
<strong>Warning: The vortex caused by the wormhole opening will
annihilate anything in its path.</strong> Vortexes can be avoided when
using sufficiently advanced dialing technology.</p>

<p><mark>An obstruction in a gate will prevent it from accepting a
wormhole connection.</mark></p>

3.10.8 The dfn element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content, but there must be no descendant dfn elements.
Element-specific attributes:
None, but the title attribute has special semantics on this element.
DOM interface:
Uses HTMLElement.

The dfn element represents the defining instance of a term. The paragraph, description list group, or section that is the nearest ancestor of the dfn element must also contain the definition(s) for the term given by the dfn element.

Defining term: If the dfn element has a title attribute, then the exact value of that attribute is the term being defined. Otherwise, if it contains exactly one element child node and no child text nodes, and that child element is an abbr element with a title attribute, then the exact value of that attribute is the term being defined. Otherwise, it is the exact textContent of the dfn element that gives the term being defined.

If the title attribute of the dfn element is present, then it must contain only the term being defined.

The title attribute of ancestor elements does not affect dfn elements.

An a element that links to a dfn element represents an instance of the term defined by the dfn element.

In the following fragment, the term "GDO" is first defined in the first paragraph, then used in the second.

<p>The <dfn><abbr title="Garage Door Opener">GDO</abbr></dfn>
is a device that allows off-world teams to open the iris.</p>
<!-- ... later in the document: -->
<p>Teal'c activated his <abbr title="Garage Door Opener">GDO</abbr>
and so Hammond ordered the iris to be opened.</p>

With the addition of an a element, the reference can be made explicit:

<p>The <dfn id=gdo><abbr title="Garage Door Opener">GDO</abbr></dfn>
is a device that allows off-world teams to open the iris.</p>
<!-- ... later in the document: -->
<p>Teal'c activated his <a href=#gdo><abbr title="Garage Door Opener">GDO</abbr></a>
and so Hammond ordered the iris to be opened.</p>

3.10.9 The abbr element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None, but the title attribute has special semantics on this element.
DOM interface:
Uses HTMLElement.

The abbr element represents an abbreviation or acronym, optionally with its expansion. The title attribute may be used to provide an expansion of the abbreviation. The attribute, if specified, must contain an expansion of the abbreviation, and nothing else.

The paragraph below contains an abbreviation marked up with the abbr element. This paragraph defines the term "Web Hypertext Application Technology Working Group".

<p>The <dfn id=whatwg><abbr title="Web Hypertext Application
Technology Working Group">WHATWG</abbr></dfn> is a loose
unofficial collaboration of Web browser manufacturers and interested
parties who wish to develop new technologies designed to allow authors
to write and deploy Applications over the World Wide Web.</p>

This paragraph has two abbreviations. Notice how only one is defined; the other, with no expansion associated with it, does not use the abbr element.

<p>The <abbr title="Web Hypertext Application Technology Working
Group">WHATWG</abbr> started working on HTML5 in 2004.</p>

This paragraph links an abbreviation to its definition.

<p>The <a href="#whatwg"><abbr title="Web Hypertext Application
Technology Working Group">WHATWG</abbr></a> community does not
have much representation from Asia.</p>

This paragraph marks up an abbreviation without giving an expansion, possibly as a hook to apply styles for abbreviations (e.g. smallcaps).

<p>Philip` and Dashiva both denied that they were going to
get the issue counts from past revisions of the specification to
backfill the <abbr>WHATWG</abbr> issue graph.</p>

If an abbreviation is pluralized, the expansion's grammatical number (plural vs singular) must match the grammatical number of the contents of the element.

Here the plural is outside the element, so the expansion is in the singular:

<p>Two <abbr title="Working Group">WG</abbr>s worked on
this specification: the <abbr>WHATWG</abbr> and the
<abbr>HTMLWG</abbr>.</p>

Here the plural is inside the element, so the expansion is in the plural:

<p>Two <abbr title="Working Groups">WGs</abbr> worked on
this specification: the <abbr>WHATWG</abbr> and the
<abbr>HTMLWG</abbr>.</p>

3.10.10 The time element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
datetime
DOM interface:
interface HTMLTimeElement : HTMLElement {
           attribute DOMString dateTime;
  readonly attribute DOMTimeStamp date;
  readonly attribute DOMTimeStamp time;
  readonly attribute DOMTimeStamp timezone;
};

The time element represents a date and/or a time.

The datetime attribute, if present, must contain a date or time string that identifies the date or time being specified.

If the datetime attribute is not present, then the date or time must be specified in the content of the element, such that parsing the element's textContent according to the rules for parsing date or time strings in content successfully extracts a date or time.

The dateTime DOM attribute must reflect the datetime content attribute.

User agents, to obtain the date, time, and timezone represented by a time element, must follow these steps:

  1. If the datetime attribute is present, then parse it according to the rules for parsing date or time strings in attributes, and let the result be result.
  2. Otherwise, parse the element's textContent according to the rules for parsing date or time strings in content, and let the result be result.
  3. If result is empty (because the parsing failed), then the date is unknown, the time is unknown, and the timezone is unknown.
  4. Otherwise: if result contains a date, then that is the date; if result contains a time, then that is the time; and if result contains a timezone, then the timezone is the element's timezone. (A timezone can only be present if both a date and a time are also present.)

The date DOM attribute must return null if the date is unknown, and otherwise must return the time corresponding to midnight UTC (i.e. the first second) of the given date.

The time DOM attribute must return null if the time is unknown, and otherwise must return the time corresponding to the given time of 1970-01-01, with the timezone UTC.

The timezone DOM attribute must return null if the timezone is unknown, and otherwise must return the time corresponding to 1970-01-01 00:00 UTC in the given timezone, with the timezone set to UTC (i.e. the time corresponding to 1970-01-01 at 00:00 UTC plus the offset corresponding to the timezone).

In the following snippet:

<p>Our first date was <time datetime="2006-09-23">a Saturday</time>.</p>

...the time element's date attribute would have the value 1,158,969,600,000ms, and the time and timezone attributes would return null.

In the following snippet:

<p>We stopped talking at <time datetime="2006-09-24 05:00 -7">5am the next morning</time>.</p>

...the time element's date attribute would have the value 1,159,056,000,000ms, the time attribute would have the value 18,000,000ms, and the timezone attribute would return −25,200,000ms. To obtain the actual time, the three attributes can be added together, obtaining 1,159,048,800,000, which is the specified date and time in UTC.

Finally, in the following snippet:

<p>Many people get up at <time>08:00</time>.</p>

...the time element's date attribute would have the value null, the time attribute would have the value 28,800,000ms, and the timezone attribute would return null.

These APIs may be suboptimal. Comments on making them more useful to JS authors are welcome. The primary use cases for these elements are for marking up publication dates e.g. in blog entries, and for marking event dates in hCalendar markup. Thus the DOM APIs are likely to be used as ways to generate interactive calendar widgets or some such.

3.10.11 The progress element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
value
max
DOM interface:
interface HTMLProgressElement : HTMLElement {
           attribute float value;
           attribute float max;
  readonly attribute float position;
};

The progress element represents the completion progress of a task. The progress is either indeterminate, indicating that progress is being made but that it is not clear how much more work remains to be done before the task is complete (e.g. because the task is waiting for a remote host to respond), or the progress is a number in the range zero to a maximum, giving the fraction of work that has so far been completed.

There are two attributes that determine the current task completion represented by the element.

The value attribute specifies how much of the task has been completed, and the max attribute specifies how much work the task requires in total. The units are arbitrary and not specified.

Instead of using the attributes, authors are recommended to include the current value and the maximum value inline as text inside the element.

Here is a snippet of a Web application that shows the progress of some automated task:

<section>
 <h2>Task Progress</h2>
 <p>Progress: <progress><span id="p">0</span>%</progress></p>
 <script>
  var progressBar = document.getElementById('p');
  function updateProgress(newValue) {
    progressBar.textContent = newValue;
  }
 </script>
</section>

(The updateProgress() method in this example would be called by some other code on the page to update the actual progress bar as the task progressed.)

Author requirements: The max and value attributes, when present, must have values that are valid floating point numbers. The max attribute, if present, must have a value greater than zero. The value attribute, if present, must have a value equal to or greater than zero, and less than or equal to the value of the max attribute, if present.

The progress element is the wrong element to use for something that is just a gauge, as opposed to task progress. For instance, indicating disk space usage using progress would be inappropriate. Instead, the meter element is available for such use cases.

User agent requirements: User agents must parse the max and value attributes' values according to the rules for parsing floating point number values.

If the value attribute is omitted, then user agents must also parse the textContent of the progress element in question using the steps for finding one or two numbers of a ratio in a string. These steps will return nothing, one number, one number with a denominator punctuation character, or two numbers.

Using the results of this processing, user agents must determine whether the progress bar is an indeterminate progress bar, or whether it is a determinate progress bar, and in the latter case, what its current and maximum values are, all as follows:

  1. If the max attribute is omitted, and the value is omitted, and the results of parsing the textContent was nothing, then the progress bar is an indeterminate progress bar. Abort these steps.
  2. Otherwise, it is a determinate progress bar.
  3. If the max attribute is included, then, if a value could be parsed out of it, then the maximum value is that value.
  4. Otherwise, if the max attribute is absent but the value attribute is present, or, if the max attribute is present but no value could be parsed from it, then the maximum is 1.
  5. Otherwise, if neither attribute is included, then, if the textContent contained one number with an associated denominator punctuation character, then the maximum value is the value associated with that denominator punctuation character; otherwise, if the textContent contained two numbers, the maximum value is the higher of the two values; otherwise, the maximum value is 1.
  6. If the value attribute is present on the element and a value could be parsed out of it, that value is the current value of the progress bar. Otherwise, if the attribute is present but no value could be parsed from it, the current value is zero.
  7. Otherwise if the value attribute is absent and the max attribute is present, then, if the textContent was parsed and found to contain just one number, with no associated denominator punctuation character, then the current value is that number. Otherwise, if the value attribute is absent and the max attribute is present then the current value is zero.
  8. Otherwise, if neither attribute is present, then the current value is the lower of the one or two numbers that were found in the textContent of the element.
  9. If the maximum value is less than or equal to zero, then it is reset to 1.
  10. If the current value is less than zero, then it is reset to zero.
  11. Finally, if the current value is greater than the maximum value, then the current value is reset to the maximum value.

UA requirements for showing the progress bar: When representing a progress element to the user, the UA should indicate whether it is a determinate or indeterminate progress bar, and in the former case, should indicate the relative position of the current value relative to the maximum value.

The max and value DOM attributes must reflect the elements' content attributes of the same name. When the relevant content attributes are absent, the DOM attributes must return zero. The value parsed from the textContent never affects the DOM values.

Would be cool to have the value DOM attribute update the textContent in-line...

If the progress bar is an indeterminate progress bar, then the position DOM attribute must return −1. Otherwise, it must return the result of dividing the current value by the maximum value.

3.10.12 The meter element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
value
min
low
high
max
optimum
DOM interface:
interface HTMLMeterElement : HTMLElement {
           attribute float value;
           attribute float min;
           attribute float max;
           attribute float low;
           attribute float high;
           attribute float optimum;
};

The meter element represents a scalar measurement within a known range, or a fractional value; for example disk usage, the relevance of a query result, or the fraction of a voting population to have selected a particular candidate.

This is also known as a gauge.

The meter element should not be used to indicate progress (as in a progress bar). For that role, HTML provides a separate progress element.

The meter element also does not represent a scalar value of arbitrary range — for example, it would be wrong to use this to report a weight, or height, unless there is a known maximum value.

There are six attributes that determine the semantics of the gauge represented by the element.

The min attribute specifies the lower bound of the range, and the max attribute specifies the upper bound. The value attribute specifies the value to have the gauge indicate as the "measured" value.

The other three attributes can be used to segment the gauge's range into "low", "medium", and "high" parts, and to indicate which part of the gauge is the "optimum" part. The low attribute specifies the range that is considered to be the "low" part, and the high attribute specifies the range that is considered to be the "high" part. The optimum attribute gives the position that is "optimum"; if that is higher than the "high" value then this indicates that the higher the value, the better; if it's lower than the "low" mark then it indicates that lower values are better, and naturally if it is in between then it indicates that neither high nor low values are good.

Authoring requirements: The recommended way of giving the value is to include it as contents of the element, either as two numbers (the higher number represents the maximum, the other number the current value, and the minimum is assumed to be zero), or as a percentage or similar (using one of the characters such as "%"), or as a fraction.

The value, min, low, high, max, and optimum attributes are all optional. When present, they must have values that are valid floating point numbers, and their values must satisfy the following inequalities:

The following examples all represent a measurement of three quarters (of the maximum of whatever is being measured):

<meter>75%</meter>
<meter>750‰</meter>
<meter>3/4</meter>
<meter>6 blocks used (out of 8 total)</meter>
<meter>max: 100; current: 75</meter>
<meter><object data="graph75.png">0.75</object></meter>
<meter min="0" max="100" value="75"></meter>

The following example is incorrect use of the element, because it doesn't give a range (and since the default maximum is 1, both of the gauges would end up looking maxed out):

<p>The grapefruit pie had a radius of <meter>12cm</meter>
and a height of <meter>2cm</meter>.</p> <!-- BAD! -->

Instead, one would either not include the meter element, or use the meter element with a defined range to give the dimensions in context compared to other pies:

<p>The grapefruit pie had a radius of 12cm and a height of
2cm.</p>
<dl>
 <dt>Radius: <dd> <meter min=0 max=20 value=12>12cm</meter>
 <dt>Height: <dd> <meter min=0 max=10 value=2>2cm</meter>
</dl>

There is no explicit way to specify units in the meter element, but the units may be specified in the title attribute in free-form text.

The example above could be extended to mention the units:

<dl>
 <dt>Radius: <dd> <meter min=0 max=20 value=12 title="centimeters">12cm</meter>
 <dt>Height: <dd> <meter min=0 max=10 value=2 title="centimeters">2cm</meter>
</dl>

User agent requirements: User agents must parse the min, max, value, low, high, and optimum attributes using the rules for parsing floating point number values.

If the value attribute has been omitted, the user agent must also process the textContent of the element according to the steps for finding one or two numbers of a ratio in a string. These steps will return nothing, one number, one number with a denominator punctuation character, or two numbers.

User agents must then use all these numbers to obtain values for six points on the gauge, as follows. (The order in which these are evaluated is important, as some of the values refer to earlier ones.)

The minimum value

If the min attribute is specified and a value could be parsed out of it, then the minimum value is that value. Otherwise, the minimum value is zero.

The maximum value

If the max attribute is specified and a value could be parsed out of it, the maximum value is that value.

Otherwise, if the max attribute is specified but no value could be parsed out of it, or if it was not specified, but either or both of the min or value attributes were specified, then the maximum value is 1.

Otherwise, none of the max, min, and value attributes were specified. If the result of processing the textContent of the element was either nothing or just one number with no denominator punctuation character, then the maximum value is 1; if the result was one number but it had an associated denominator punctuation character, then the maximum value is the value associated with that denominator punctuation character; and finally, if there were two numbers parsed out of the textContent, then the maximum is the higher of those two numbers.

If the above machinations result in a maximum value less than the minimum value, then the maximum value is actually the same as the minimum value.

The actual value

If the value attribute is specified and a value could be parsed out of it, then that value is the actual value.

If the value attribute is not specified but the max attribute is specified and the result of processing the textContent of the element was one number with no associated denominator punctuation character, then that number is the actual value.

If neither of the value and max attributes are specified, then, if the result of processing the textContent of the element was one number (with or without an associated denominator punctuation character), then that is the actual value, and if the result of processing the textContent of the element was two numbers, then the actual value is the lower of the two numbers found.

Otherwise, if none of the above apply, the actual value is zero.

If the above procedure results in an actual value less than the minimum value, then the actual value is actually the same as the minimum value.

If, on the other hand, the result is an actual value greater than the maximum value, then the actual value is the maximum value.

The low boundary

If the low attribute is specified and a value could be parsed out of it, then the low boundary is that value. Otherwise, the low boundary is the same as the minimum value.

If the above results in a low boundary that is less than the minimum value, the low boundary is the minimum value.

The high boundary

If the high attribute is specified and a value could be parsed out of it, then the high boundary is that value. Otherwise, the high boundary is the same as the maximum value.

If the above results in a high boundary that is higher than the maximum value, the high boundary is the maximum value.

The optimum point

If the optimum attribute is specified and a value could be parsed out of it, then the optimum point is that value. Otherwise, the optimum point is the midpoint between the minimum value and the maximum value.

If the optimum point is then less than the minimum value, then the optimum point is actually the same as the minimum value. Similarly, if the optimum point is greater than the maximum value, then it is actually the maximum value instead.

All of which should result in the following inequalities all being true:

UA requirements for regions of the gauge: If the optimum point is equal to the low boundary or the high boundary, or anywhere in between them, then the region between the low and high boundaries of the gauge must be treated as the optimum region, and the low and high parts, if any, must be treated as suboptimal. Otherwise, if the optimum point is less than the low boundary, then the region between the minimum value and the low boundary must be treated as the optimum region, the region between the low boundary and the high boundary must be treated as a suboptimal region, and the region between the high boundary and the maximum value must be treated as an even less good region. Finally, if the optimum point is higher than the high boundary, then the situation is reversed; the region between the high boundary and the maximum value must be treated as the optimum region, the region between the high boundary and the low boundary must be treated as a suboptimal region, and the remaining region between the low boundary and the minimum value must be treated as an even less good region.

UA requirements for showing the gauge: When representing a meter element to the user, the UA should indicate the relative position of the actual value to the minimum and maximum values, and the relationship between the actual value and the three regions of the gauge.

The following markup:

<h3>Suggested groups</h3>
<menu type="toolbar">
 <a href="?cmd=hsg" onclick="hideSuggestedGroups()">Hide suggested groups</a>
</menu>
<ul>
 <li>
  <p><a href="/group/comp.infosystems.www.authoring.stylesheets/view">comp.infosystems.www.authoring.stylesheets</a> -
     <a href="/group/comp.infosystems.www.authoring.stylesheets/subscribe">join</a></p>
  <p>Group description: <strong>Layout/presentation on the WWW.</strong></p>
  <p><meter value="0.5">Moderate activity,</meter> Usenet, 618 subscribers</p>
 </li>
 <li>
  <p><a href="/group/netscape.public.mozilla.xpinstall/view">netscape.public.mozilla.xpinstall</a> -
     <a href="/group/netscape.public.mozilla.xpinstall/subscribe">join</a></p>
  <p>Group description: <strong>Mozilla XPInstall discussion.</strong></p>
  <p><meter value="0.25">Low activity,</meter> Usenet, 22 subscribers</p>
 </li>
 <li>
  <p><a href="/group/mozilla.dev.general/view">mozilla.dev.general</a> -
     <a href="/group/mozilla.dev.general/subscribe">join</a></p>
  <p><meter value="0.25">Low activity,</meter> Usenet, 66 subscribers</p>
 </li>
</ul>

Might be rendered as follows:

With the <meter> elements rendered as inline green bars of
    varying lengths.

User agents may combine the value of the title attribute and the other attributes to provide context-sensitive help or inline text detailing the actual values.

For example, the following snippet:

<meter min=0 max=60 value=23.2 title=seconds></meter>

...might cause the user agent to display a gauge with a tooltip saying "Value: 23.2 out of 60." on one line and "seconds" on a second line.

The min, max, value, low, high, and optimum DOM attributes must reflect the elements' content attributes of the same name. When the relevant content attributes are absent, the DOM attributes must return zero. The value parsed from the textContent never affects the DOM values.

Would be cool to have the value DOM attribute update the textContent in-line...

3.10.13 The code element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The code element represents a fragment of computer code. This could be an XML element name, a filename, a computer program, or any other string that a computer would recognize.

Although there is no formal way to indicate the language of computer code being marked up, authors who wish to mark code elements with the language used, e.g. so that syntax highlighting scripts can use the right rules, may do so by adding a class prefixed with "language-" to the element.

The following example shows how the element can be used in a paragraph to mark up element names and computer code, including punctuation.

<p>The <code>code</code> element represents a fragment of computer
code.</p>

<p>When you call the <code>activate()</code> method on the
<code>robotSnowman</code> object, the eyes glow.</p>

<p>The example below uses the <code>begin</code> keyword to indicate
the start of a statement block. It is paired with an <code>end</code>
keyword, which is followed by the <code>.</code> punctuation character
(full stop) to indicate the end of the program.</p>

The following example shows how a block of code could be marked up using the pre and code elements.

<pre><code class="language-pascal">var i: Integer;
begin
   i := 1;
end.</code></pre>

A class is used in that example to indicate the language used.

See the pre element for more details.

3.10.14 The var element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The var element represents a variable. This could be an actual variable in a mathematical expression or programming context, or it could just be a term used as a placeholder in prose.

In the paragraph below, the letter "n" is being used as a variable in prose:

<p>If there are <var>n</var> pipes leading to the ice
cream factory then I expect at <em>least</em> <var>n</var>
flavours of ice cream to be available for purchase!</p>

3.10.15 The samp element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The samp element represents (sample) output from a program or computing system.

See the pre and kbd elements for more details.

This example shows the samp element being used inline:

<p>The computer said <samp>Too much cheese in tray
two</samp> but I didn't know what that meant.</p>

This second example shows a block of sample output. Nested samp and kbd elements allow for the styling of specific elements of the sample output using a style sheet.

<pre><samp><samp class="prompt">jdoe@mowmow:~$</samp> <kbd>ssh demo.example.com</kbd>
Last login: Tue Apr 12 09:10:17 2005 from mowmow.example.com on pts/1
Linux demo 2.6.10-grsec+gg3+e+fhs6b+nfs+gr0501+++p3+c4a+gr2b-reslog-v6.189 #1 SMP Tue Feb 1 11:22:36 PST 2005 i686 unknown

<samp class="prompt">jdoe@demo:~$</samp> <samp class="cursor">_</samp></samp></pre>

3.10.16 The kbd element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The kbd element represents user input (typically keyboard input, although it may also be used to represent other input, such as voice commands).

When the kbd element is nested inside a samp element, it represents the input as it was echoed by the system.

When the kbd element contains a samp element, it represents input based on system output, for example invoking a menu item.

When the kbd element is nested inside another kbd element, it represents an actual key or other single unit of input as appropriate for the input mechanism.

Here the kbd element is used to indicate keys to press:

<p>To make George eat an apple, press <kbd><kbd>Shift</kbd>+<kbd>F3</kbd></kbd></p>

In this second example, the user is told to pick a particular menu item. The outer kbd element marks up a block of input, with the inner kbd elements representing each individual step of the input, and the samp elements inside them indicating that the steps are input based on something being displayed by the system, in this case menu labels:

<p>To make George eat an apple, select
    <kbd><kbd><samp>File</samp></kbd>|<kbd><samp>Eat Apple...</samp></kbd></kbd>
</p>

3.10.17 The sub and sup elements

Categories
Phrasing content.
Contexts in which these elements may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The sup element represents a superscript and the sub element represents a subscript.

These elements must be used only to mark up typographical conventions with specific meanings, not for typographical presentation for presentation's sake. For example, it would be inappropriate for the sub and sup elements to be used in the name of the LaTeX document preparation system. In general, authors should use these elements only if the absence of those elements would change the meaning of the content.

When the sub element is used inside a var element, it represents the subscript that identifies the variable in a family of variables.

<p>The coordinate of the <var>i</var>th point is
(<var>x<sub><var>i</var></sub></var>, <var>y<sub><var>i</var></sub></var>).
For example, the 10th point has coordinate
(<var>x<sub>10</sub></var>, <var>y<sub>10</sub></var>).</p>

In certain languages, superscripts are part of the typographical conventions for some abbreviations.

<p>The most beautiful women are
<span lang="fr"><abbr>M<sup>lle</sup></abbr> Gwendoline</span> and 
<span lang="fr"><abbr>M<sup>me</sup></abbr> Denise</span>.</p>

Mathematical expressions often use subscripts and superscripts. Authors are encouraged to use MathML for marking up mathematics, but authors may opt to use sub and sup if detailed mathematical markup is not desired. [MathML]

<var>E</var>=<var>m</var><var>c</var><sup>2</sup>
f(<var>x</var>, <var>n</var>) = log<sub>4</sub><var>x</var><sup><var>n</var></sup>

3.10.18 The span element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The span element doesn't mean anything on its own, but can be useful when used together with other attributes, e.g. class, lang, or dir.

3.10.19 The i element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The i element represents a span of text in an alternate voice or mood, or otherwise offset from the normal prose, such as a taxonomic designation, a technical term, an idiomatic phrase from another language, a thought, a ship name, or some other prose whose typical typographic presentation is italicized.

Terms in languages different from the main text should be annotated with lang attributes (xml:lang in XML).

The examples below show uses of the i element:

<p>The <i class="taxonomy">Felis silvestris catus</i> is cute.</p>
<p>The term <i>prose content</i> is defined above.</p>
<p>There is a certain <i lang="fr">je ne sais quoi</i> in the air.</p>

In the following example, a dream sequence is marked up using i elements.

<p>Raymond tried to sleep.</p>
<p><i>The ship sailed away on Thursday</i>, he
dreamt. <i>The ship had many people aboard, including a beautiful
princess called Carey. He watched her, day-in, day-out, hoping she
would notice him, but she never did.</i></p>
<p><i>Finally one night he picked up the courage to speak with
her—</i></p>
<p>Raymond woke with a start as the fire alarm rang out.</p>

The i element should be used as a last resort when no other element is more appropriate. In particular, citations should use the cite element, defining instances of terms should use the dfn element, stress emphasis should use the em element, importance should be denoted with the strong element, quotes should be marked up with the q element, and small print should use the small element.

Authors are encouraged to use the class attribute on the i element to identify why the element is being used, so that if the style of a particular use (e.g. dream sequences as opposed to taxonomic terms) is to be changed at a later date, the author doesn't have to go through the entire document (or series of related documents) annotating each use.

Style sheets can be used to format i elements, just like any other element can be restyled. Thus, it is not the case that content in i elements will necessarily be italicized.

3.10.20 The b element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The b element represents a span of text to be stylistically offset from the normal prose without conveying any extra importance, such as key words in a document abstract, product names in a review, or other spans of text whose typical typographic presentation is boldened.

The following example shows a use of the b element to highlight key words without marking them up as important:

<p>The <b>frobonitor</b> and <b>barbinator</b> components are fried.</p>

In the following example, objects in a text adventure are highlighted as being special by use of the b element.

<p>You enter a small room. Your <b>sword</b> glows
brighter. A <b>rat</b> scurries past the corner wall.</p>

Another case where the b element is appropriate is in marking up the lede (or lead) sentence or paragraph. The following example shows how a BBC article about kittens adopting a rabbit as their own could be marked up using HTML5 elements:

<article>
 <h2>Kittens 'adopted' by pet rabbit</h2>
 <p><b>Six abandoned kittens have found an unexpected new
 mother figure — a pet rabbit.</b></p>
 <p>Veterinary nurse Melanie Humble took the three-week-old
 kittens to her Aberdeen home.</p>
[...]

The b element should be used as a last resort when no other element is more appropriate. In particular, headers should use the h1 to h6 elements, stress emphasis should use the em element, importance should be denoted with the strong element, and text marked or highlighted should use the mark element.

The following would be incorrect usage:

<p><b>WARNING!</b> Do not frob the barbinator!</p>

In the previous example, the correct element to use would have been strong, not b.

Style sheets can be used to format b elements, just like any other element can be restyled. Thus, it is not the case that content in b elements will necessarily be boldened.

3.10.21 The bdo element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
Phrasing content.
Element-specific attributes:
None, but the dir global attribute has special requirements on this element.
DOM interface:
Uses HTMLElement.

The bdo element allows authors to override the Unicode bidi algorithm by explicitly specifying a direction override. [BIDI]

Authors must specify the dir attribute on this element, with the value ltr to specify a left-to-right override and with the value rtl to specify a right-to-left override.

If the element has the dir attribute set to the exact value ltr, then for the purposes of the bidi algorithm, the user agent must act as if there was a U+202D LEFT-TO-RIGHT OVERRIDE character at the start of the element, and a U+202C POP DIRECTIONAL FORMATTING at the end of the element.

If the element has the dir attribute set to the exact value rtl, then for the purposes of the bidi algorithm, the user agent must act as if there was a U+202E RIGHT-TO-LEFT OVERRIDE character at the start of the element, and a U+202C POP DIRECTIONAL FORMATTING at the end of the element.

The requirements on handling the bdo element for the bidi algorithm may be implemented indirectly through the style layer. For example, an HTML+CSS user agent should implement these requirements by implementing the CSS unicode-bidi property. [CSS21]

3.10.22 The ruby element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected.
Content model:
One or more groups of: phrasing content followed either by a single rt element, or an rp element, an rt element, and another rp element.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The ruby element allows one or more spans of phrasing content to be marked with ruby annotations.

A ruby element represents the spans of phrasing content it contains, ignoring all the child rt and rp elements and their descendants. Those spans of phrasing content have associated annotations created using the rt element.

In this example, each ideograph in the text 斎藤信男 is annotated with its reading.

... <ruby>
 斎 <rt> さい </rt>
 藤 <rt> とう </rt>
 信 <rt> のぶ </rt>
 男 <rt> お         </rt>
</ruby> ...

This might be rendered as:

The four main ideographs, each with its reading annotation
    rendered in a smaller font above it.

3.10.23 The rt element

Categories
None.
Contexts in which this element may be used:
As a child of a ruby element.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The rt element marks the ruby text component of a ruby annotation.

An rt element that is a child of a ruby element represents an annotation (given by its children) for the zero or more nodes of phrasing content that immediately precedes it in the ruby element, ignoring rp elements.

An rt element that is not a child of a ruby element represents the same thing as its children.

3.10.24 The rp element

Categories
None.
Contexts in which this element may be used:
As a child of a ruby element, either immediately before or immediately after an rt element.
Content model:
If the rp element is immediately after an rt element that is immediately preceded by another rp element: a single character from Unicode character class Pe.
Otherwise: a single character from Unicode character class Ps.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The rp element can be used to provide parentheses around a ruby text component of a ruby annotation, to be shown by user agents that don't support ruby annotations.

An rp element that is a child of a ruby element represents nothing and it and its contents must be ignored. An rp element whose parent element is not a ruby element represents the same thing as its children.

The example above, in which each ideograph in the text 斎藤信男 is annotated with its reading, could be expanded to use rp so that in legacy user agentthe readings are in parentheses:

... <ruby>
 斎 <rp>(</rp><rt>さい</rt><rp>)</rp>
 藤 <rp>(</rp><rt>とう</rt><rp>)</rp>
 信 <rp>(</rp><rt>のぶ</rt><rp>)</rp>
 男 <rp>(</rp><rt>お</rt><rp>)</rp>
</ruby> ...

In conforming user agents the rendering would be as above, but in user agents that do not support ruby, the rendering would be:

... 斎 (さい) 藤 (とう) 信 (のぶ) 男 (お) ...

3.10.25 Usage summary

We need to summarize the various elements, in particular to distinguish b/i/em/strong/var/q/mark/cite.

3.10.26 Footnotes

HTML does not have a dedicated mechanism for marking up footnotes. Here are the recommended alternatives.

For short inline annotations, the title attribute should be used.

In this example, two parts of a dialog are annotated.

<dialog>
 <dt>Customer
 <dd>Hello! I wish to register a complaint. Hello. Miss?
 <dt>Shopkeeper
 <dd><span title="Colloquial pronunciation of 'What do you'"
 >Watcha</span> mean, miss?
 <dt>Customer
 <dd>Uh, I'm sorry, I have a cold. I wish to make a complaint.
 <dt>Shopkeeper
 <dd>Sorry, <span title="This is, of course, a lie.">we're
 closing for lunch</span>.
</dialog>

For longer annotations, the a element should be used, pointing to an element later in the document. The convention is that the contents of the link be a number in square brackets.

In this example, a footnote in the dialog links to a paragraph below the dialog. The paragraph then reciprocally links back to the dialog, allowing the user to return to the location of the footnote.

<dialog>
 <dt>Announcer
 <dd>Number 16: The <i>hand</i>.
 <dt>Interviewer
 <dd>Good evening. I have with me in the studio tonight Mr
 Norman St John Polevaulter, who for the past few years has
 been contradicting people. Mr Polevaulter, why <em>do</em>
 you contradict people?
 <dt>Norman
 <dd>I don't. <a href="#fn1" id="r1">[1]</a>
 <dt>Interviewer
 <dd>You told me you did!
</dialog>
<section>
 <p id="fn1"><a href="#r1">[1]</a> This is, naturally, a lie,
 but paradoxically if it were true he could not say so without
 contradicting the interviewer and thus making it false.</p>
</section>

For side notes, longer annotations that apply to entire sections of the text rather than just specific words or sentences, the aside element should be used.

In this example, a sidebar is given after a dialog, giving some context to the dialog.

<dialog>
 <dt>Customer
 <dd>I will not buy this record, it is scratched.
 <dt>Shopkeeper
 <dd>I'm sorry?
 <dt>Customer
 <dd>I will not buy this record, it is scratched.
 <dt>Shopkeeper
 <dd>No no no, this's'a tobacconist's.
</dialog>
<aside>
 <p>In 1970, the British Empire lay in ruins, and foreign
 nationalists frequented the streets — many of them Hungarians
 (not the streets — the foreign nationals). Sadly, Alexander
 Yalt has been publishing incompetently-written phrase books.
</aside>

3.11 Edits

The ins and del elements represent edits to the document.

3.11.1 The ins element

Categories
When the element only contains phrasing content: phrasing content.
Otherwise: flow content.
Contexts in which this element may be used:
When the element only contains phrasing content: where phrasing content is expected.
Otherwise: where flow content is expected.
Content model:
Transparent.
Element-specific attributes:
cite
datetime
DOM interface:
Uses the HTMLModElement interface.

The ins element represents an addition to the document.

The following represents the addition of a single paragraph:

<aside>
 <ins>
  <p> I like fruit. </p>
 </ins>
</aside>

As does this, because everything in the aside element here counts as phrasing content and therefore there is just one paragraph:

<aside>
 <ins>
  Apples are <em>tasty</em>.
 </ins>
 <ins>
  So are pears.
 </ins>
</aside>

ins elements should not cross implied paragraph boundaries.

The following example represents the addition of two paragraphs, the second of which was inserted in two parts. The first ins element in this example thus crosses a paragraph boundary, which is considered poor form.

<aside>
 <ins datetime="2005-03-16T00:00Z">
  <p> I like fruit. </p>
  Apples are <em>tasty</em>.
 </ins>
 <ins datetime="2007-12-19T00:00Z">
  So are pears.
 </ins>
</aside>

Here is a better way of marking this up. It uses more elements, but none of the elements cross implied paragraph boundaries.

<aside>
 <ins datetime="2005-03-16T00:00Z">
  <p> I like fruit. </p>
 </ins>
 <ins datetime="2005-03-16T00:00Z">
  Apples are <em>tasty</em>.
 </ins>
 <ins datetime="2007-12-19T00:00Z">
  So are pears.
 </ins>
</aside>

3.11.2 The del element

Categories
When the element only contains phrasing content: phrasing content.
Otherwise: flow content.
Contexts in which this element may be used:
When the element only contains phrasing content: where phrasing content is expected.
Otherwise: where flow content is expected.
Content model:
Transparent.
Element-specific attributes:
cite
datetime
DOM interface:
Uses the HTMLModElement interface.

The del element represents a removal from the document.

del elements should not cross implied paragraph boundaries.

3.11.3 Attributes common to ins and del elements

The cite attribute may be used to specify a URI that explains the change. When that document is long, for instance the minutes of a meeting, authors are encouraged to include a fragment identifier pointing to the specific part of that document that discusses the change.

If the cite attribute is present, it must be a URI (or IRI) that explains the change. User agents should allow users to follow such citation links.

The datetime attribute may be used to specify the time and date of the change.

If present, the datetime attribute must be a valid datetime value.

User agents must parse the datetime attribute according to the parse a string as a datetime value algorithm. If that doesn't return a time, then the modification has no associated timestamp (the value is non-conforming; it is not a valid datetime). Otherwise, the modification is marked as having been made at the given datetime. User agents should use the associated timezone information to determine which timezone to present the given datetime in.

The ins and del elements must implement the HTMLModElement interface:

interface HTMLModElement : HTMLElement {
           attribute DOMString cite;
           attribute DOMString dateTime;
};

The cite DOM attribute must reflect the element's cite content attribute. The dateTime DOM attribute must reflect the element's datetime content attribute.

3.11.4 Edits and paragraphs

Since the ins and del elements do not affect paragraphing, it is possible, in some cases where paragraphs are implied (without explicit p elements), for an ins or del element to span both an entire paragraph or other non-phrasing content elements and part of another paragraph.

For example:

<section>
 <ins>
  <p>
   This is a paragraph that was inserted.
  </p>
  This is another paragraph whose first sentence was inserted
  at the same time as the paragraph above.
 </ins>
 This is a second sentence, which was there all along.
</section>

By only wrapping some paragraphs in p elements, one can even get the end of one paragraph, a whole second paragraph, and the start of a third paragraph to be covered by the same ins or del element (though this is very confusing, and not considered good practice):

<section>
 This is the first paragraph. <ins>This sentence was
 inserted.
 <p>This second paragraph was inserted.</p>
 This sentence was inserted too.</ins> This is the
 third paragraph in this example.
</section>

However, due to the way implied paragraphs are defined, it is not possible to mark up the end of one paragraph and the start of the very next one using the same ins or del element. You instead have to use one (or two) p element(s) and two ins or del elements:

For example:

<section>
 <p>This is the first paragraph. <del>This sentence was
 deleted.</del></p>
 <p><del>This sentence was deleted too.</del> That
 sentence needed a separate &lt;del&gt; element.</p>
</section>

Partly because of the confusion described above, authors are strongly recommended to always mark up all paragraphs with the p element, and to not have any ins or del elements that cross across any implied paragraphs.

3.11.5 Edits and lists

The content models of the ol and ul elements do not allow ins and del elements as children. Lists always represent all their items, including items that would otherwise have been marked as deleted.

To indicate that an item is inserted or deleted, an ins or del element can be wrapped around the contents of the li element. To indicate that an item has been replaced by another, a single li element can have one or more del elements followed by one or more ins elements.

In the following example, a list that started empty had items added and removed from it over time. The bits in the example that have been emphasised show the parts that are the "current" state of the list. The list item numbers don't take into account the edits, though.

<h1>Stop-ship bugs</h1>
<ol>
 <li><ins datetime="2008-02-12 15:20 Z">Bug 225: Rain detector
 doesn't work in snow</ins></li>
 <li><del datetime="2008-03-01 20:22 Z"><ins datetime="2008-02-14 
 12:02 Z">Bug 228: Water buffer overflows in April</ins></del></li>
 <li><ins datetime="2008-02-16 13:50 Z">Bug 230: Water heater
 doesn't use renewable fuels</ins></li>
 <li><del datetime="2008-02-20 21:15 Z"><ins datetime="2008-02-16
 14:25 Z">Bug 232: Carbon dioxide emissions detected after
 startup</ins></del></li>
</ol>

In the following example, a list that started with just fruit was replaced by a list with just colors.

<h1>List of <del>fruits</del><ins>colors</ins></h1>
<ul>
 <li><del>Lime</del><ins>Green</ins></li>
 <li><del>Apple</del></li>
 <li>Orange</li>
 <li><del>Pear</del></li>
 <li><ins>Teal</ins></li>
 <li><del>Lemon</del><ins>Yellow</ins></li>
 <li>Olive</li>
 <li><ins>Purple</ins>
</ul>

3.12 Embedded content

3.12.1 The figure element

Categories
Flow content.
Sectioning root.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Either: one legend element followed by flow content.
Or: Flow content followed by one legend element.
Or: Flow content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The figure element represents some flow content, optionally with a caption, which can be moved away from the main flow of the document without affecting the document's meaning.

The element can thus be used to annotate illustrations, diagrams, photos, code listings, etc, that are referred to from the main content of the document, but that could, without affecting the flow of the document, be moved away from that primary content, e.g. to the side of the page, to dedicated pages, or to an appendix.

The first legend element child of the element, if any, represents the caption of the figure element's contents. If there is no child legend element, then there is no caption.

The remainder of the element's contents, if any, represents the content.

This example shows the figure element to mark up a code listing.

<p>In <a href="#l4">listing 4</a> we see the primary core interface
API declaration.</p>
<figure id="l4">
 <legend>Listing 4. The primary core interface API declaration.</legend>
 <pre><code>interface PrimaryCore {
  boolean verifyDataLine();
  void sendData(in sequence&lt;byte> data);
  void initSelfDestruct();
}</code></pre>
</figure>
<p>The API is designed to use UTF-8.</p>

Here we see a figure element to mark up a photo.

<figure>
 <img src="bubbles-work.jpeg"
      alt="Bubbles, sitting in his office chair, works on his
           latest project intently.">
 <legend>Bubbles at work</legend>
</figure>

In this example, we see an image that is not a figure, as well as an image and a video that are.

<h2>Malinko's comics</h2>

<p>This case centered on some sort of "intellectual property"
infringement related to a comic (see Exhibit A). The suit started
after a trailer ending with these words:</p>

<img src="promblem-packed-action.png" alt="ROUGH COPY! Promblem-Packed Action!">

<p>...was aired. A lawyer, armed with a Bigger Notebook, launched a
preemptive strike using snowballs. A complete copy of the trailer is
included with Exhibit B.</p>

<figure>
 <img src="ex-a.png" alt="Two squiggles on a dirty piece of paper.">
 <legend>Exhibit A. The alleged <cite>rough copy</cite> comic.</legend>
</figure>

<figure>
 <video src="ex-b.mov"></video>
 <legend>Exhibit A. The alleged <cite>rough copy</cite> comic.</legend>
</figure>

<p>The case was resolved out of court.</p>

Here, a part of a poem is marked up using figure.

<figure>
 <p>'Twas brillig, and the slithy toves<br>
Did gyre and gimble in the wabe;<br>
All mimsy were the borogoves,<br>
And the mome raths outgrabe.</p>
 <legend><cite>Jabberwocky</cite> (first verse). Lewis Carroll, 1832-98</legend>
</figure>

In this example, which could be part of a much larger work discussing a castle, the figure has three images in it.

<figure>
 <img src="castle1423.jpeg" title="Etching. Anonymous, ca. 1423."
      alt="The castle has one tower, and a tall wall around it.">
 <img src="castle1858.jpeg" title="Oil-based paint on canvas. Maria Towle, 1858."
      alt="The castle now has two towers and two walls.">
 <img src="castle1999.jpeg" title="Film photograph. Peter Jankle, 1999."
      alt="The castle lies in ruins, the original tower all that remains in one piece.">
 <legend>The castle through the ages: 1423, 1858, and 1999 respectively.</legend>
</figure>

3.12.2 The img element

Categories
Embedded content.
Contexts in which this element may be used:
Where embedded content is expected.
Content model:
Empty.
Element-specific attributes:
alt
src
usemap
ismap
width
height
DOM interface:
interface HTMLImageElement : HTMLElement {
           attribute DOMString alt;
           attribute DOMString src;
           attribute DOMString useMap;
           attribute boolean isMap;
           attribute long width;
           attribute long height;
  readonly attribute boolean complete;
};

An instance of HTMLImageElement can be obtained using the Image constructor.

An img element represents an image.

The image given by the src attribute is the embedded content, and the value of the alt attribute is the img element's fallback content.

Authoring requirements: The src attribute must be present, and must contain a URI (or IRI).

Should we restrict the URI to pointing to an image? What's an image? Is PDF an image? (Safari supports PDFs in <img> elements.) How about SVG? (Opera supports those). WMFs? XPMs? HTML?

The requirements for the alt attribute depend on what the image is intended to represent:

A phrase or paragraph with an alternative graphical representation

Sometimes something can be more clearly stated in graphical form, for example as a flowchart, a diagram, a graph, or a simple map showing directions. In such cases, an image can be given using the img element, but the lesser textual version must still be given, so that users who are unable to view the image (e.g. because they have a very slow connection, or because they are using a text-only browser, or because they are listening to the page being read out by a hands-free automobile voice Web browser, or simply because they are blind) are still able to understand the message being conveyed.

The text must be given in the alt attribute, and must convey the same message as the image specified in the src attribute.

In the following example we have a flowchart in image form, with text in the alt attribute rephrasing the flowchart in prose form:

<p>In the common case, the data handled by the tokenisation stage
comes from the network, but it can also come from script.</p>
<p><img src="images/parsing-model-overview.png" alt="The network
passes data to the Tokeniser stage, which passes data to the Tree
Construction stage. From there, data goes to both the DOM and to
Script Execution. Script Execution is linked to the DOM, and, using
document.write(), passes data to the Tokeniser."></p>

Here's another example, showing a good solution and a bad solution to the problem of including an image in a description.

First, here's the good solution. This sample shows how the alternative text should just be what you would have put in the prose if the image had never existed.

<!-- This is the correct way to do things. -->
<p>
 You are standing in an open field west of a house.
 <img src="house.jpeg" alt="The house is white, with a boarded front door.">
 There is a small mailbox here.
</p>

Second, here's the bad solution. In this incorrect way of doing things, the alternative text is simply a description of the image, instead of a textual replacement for the image. It's bad because when the image isn't shown, the text doesn't flow as well as in the first example.

<!-- This is the wrong way to do things. -->
<p>
 You are standing in an open field west of a house.
 <img src="house.jpeg" alt="A white house, with a boarded front door.">
 There is a small mailbox here.
</p>

It is important to realize that the alternative text is a replacement for the image, not a description of the image.

Icons: a short phrase or label with an alternative graphical representation

A document can contain information in iconic form. The icon is intended to help users of visual browsers to recognize features at a glance.

In some cases, the icon is supplemental to a text label conveying the same meaning. In those cases, the alt attribute must be present but must be empty.

Here the icons are next to text that conveys the same meaning, so they have an empty alt attribute:

<nav>
 <p><a href="/help/"><img src="/icons/help.png" alt=""> Help</a></p>
 <p><a href="/configure/"><img src="/icons/configuration.png" alt="">
 Configuration Tools</a></p>
</nav>

In other cases, the icon has no text next to it describing what it means; the icon is supposed to be self-explanatory. In those cases, an equivalent textual label must be given in the alt attribute.

Here, posts on a news site are labeled with an icon indicating their topic.

<body>
 <article>
  <header>
   <h1>Ratatouille wins <i>Best Movie of the Year</i> award</h1>
   <p><img src="movies.png" alt="Movies"></p>
  </header>
  <p>Pixar has won yet another <i>Best Movie of the Year</i> award,
  making this its 8th win in the last 12 years.</p>
 </article>
 <article>
  <header>
   <h1>Latest TWiT episode is online</h1>
   <p><img src="podcasts.png" alt="Podcasts"></p>
  </header>
  <p>The latest TWiT episode has been posted, in which we hear
  several tech news stories as well as learning much more about the
  iPhone. This week, the panelists compare how reflective their
  iPhones' Apple logos are.</p>
 </article>
</body>

Many pages include logos, insignia, flags, or emblems, which stand for a particular entity such as a company, organization, project, band, software package, country, or some such.

If the logo is being used to represent the entity, the alt attribute must contain the name of the entity being represented by the logo. The alt attribute must not contain text like the word "logo", as it is not the fact that it is a logo that is being conveyed, it's the entity itself.

If the logo is being used next to the name of the entity that it represents, then the logo is supplemental, and its alt attribute must instead be empty.

If the logo is merely used as decorative material (as branding, or, for example, as a side image in an article that mentions the entity to which the logo belongs), then the entry below on purely decorative images applies. If the logo is actually being discussed, then it is being used as a phrase or paragraph (the description of the logo) with an alternative graphical representation (the logo itself), and the first entry above applies.

In the following snippets, all four of the above cases are present. First, we see a logo used to represent a company:

<h1><img src="XYZ.gif" alt="The XYZ company"></h1>

Next, we see a paragraph which uses a logo right next to the company name, and so doesn't have any alternative text:

<article>
 <h2>News</h2>
 <p>We have recently been looking at buying the <img src="alpha.gif"
 alt=""> ΑΒΓ company, a small Greek company
 specializing in our type of product.</p>

In this third snippet, we have a logo being used in an aside, as part of the larger article discussing the acquisition:

 <aside><p><img src="alpha-large.gif" alt=""></p></aside>
 <p>The ΑΒΓ company has had a good quarter, and our
 pie chart studies of their accounts suggest a much bigger blue slice
 than its green and orange slices, which is always a good sign.</p>
</article>

Finally, we have an opinion piece talking about a logo, and the logo is therefore described in detail in the alternative text.

<p>Consider for a moment their logo:</p>

<p><img src="/images/logo" alt="It consists of a green circle with a
green question mark centered inside it."></p>

<p>How unoriginal can you get? I mean, oooooh, a question mark, how
<em>revolutionary</em>, how utterly <em>ground-breaking</em>, I'm
sure everyone will rush to adopt those specifications now! They could
at least have tried for some sort of, I don't know, sequence of
rounded squares with varying shades of green and bold white outlines,
at least that would look good on the cover of a blue book.</p>

This example shows how the alternative text should be written such that if the image isn't available, and the text is used instead, the text flows seamlessly into the surrounding text, as if the image had never been there in the first place.

A graphical representation of some of the surrounding text

In many cases, the image is actually just supplementary, and its presence merely reinforces the surrounding text. In these cases, the alt attribute must be present but its value must be the empty string.

A flowchart that repeats the previous paragraph in graphical form:

<p>The network passes data to the Tokeniser stage, which
passes data to the Tree Construction stage. From there, data goes
to both the DOM and to Script Execution. Script Execution is
linked to the DOM, and, using document.write(), passes data to
the Tokeniser.</p>
<p><img src="images/parsing-model-overview.png" alt=""></p>

A graph that repeats the previous paragraph in graphical form:

<p>According to a study covering several billion pages,
about 62% of documents on the Web in 2007 triggered the Quirks
rendering mode of Web browsers, about 30% triggered the Almost
Standards mode, and about 9% triggered the Standards mode.</p>
<p><img src="rendering-mode-pie-chart.png" alt=""></p>

In general, an image falls into this category if removing the image doesn't make the page any less useful, but including the image makes it a lot easier for users of visual browsers to understand the concept.

A purely decorative image that doesn't add any information but is still specific to the surrounding content

In some cases, the image isn't discussed by the surrounding text, but it has some relevance. Such images are decorative, but still form part of the content. In these cases, the alt attribute must be present but its value must be the empty string.

Examples where the image is purely decorative despite being relevant would include things like a photo of the Black Rock City landscape in a blog post about an event at Burning Man, or an image of a painting inspired by a poem, on a page reciting that poem. The following snippet shows an example of the latter case (only the first verse is included in this snippet):

<h1>The Lady of Shalott</h1>
<p><img src="shalott.jpeg" alt=""></p>
<p>On either side the river lie<br>
Long fields of barley and of rye,<br>
That clothe the wold and meet the sky;<br>
And through the field the road run by<br>
To many-tower'd Camelot;<br>
And up and down the people go,<br>
Gazing where the lilies blow<br>
Round an island there below,<br>
The island of Shalott.</p>

In general, if an image is decorative but isn't especially page-specific, for example an image that forms part of a site-wide design scheme, the image should be specified in the site's CSS, not in the markup of the document.

A key part of the content

In some cases, the image is a critical part of the content. This could be the case, for instance, on a page that is part of a photo gallery. The image is the whole point of the page containing it.

When it is possible for alternative text to be provided, for example if the image is part of a series of screenshots in a magazine review, or part of a comic strip, or is a photograph in a blog entry about that photograph, text that conveys can serve as a substitute for the image must be given as the contents of the alt attribute.

In a rare subset of these cases, there might be no alternative text available. This could be the case, for instance, on a photo upload site, if the site has received 8000 photos from a user without the user annotating any of them. In such cases, the alt attribute may be omitted, but the alt attribute should be included, with a useful value, if at all possible.

In any case, if an image is a key part of the content, the alt attribute must not be specified with an empty value.

A screenshot in a gallery of screenshots for a new OS, with some alternative text:

<figure>
 <img src="KDE%20Light%20desktop.png"
      alt="The desktop is blue, with icons along the left hand side in
           two columns, reading System, Home, K-Mail, etc. A window is
           open showing that menus wrap to a second line if they
           cannot fit in the window. The window has a list of icons
           along the top, with an address bar below it, a list of
           icons for tabs along the left edge, a status bar on the
           bottom, and two panes in the middle. The desktop has a bar
           at the bottom of the screen with a few buttons, a pager, a
           list of open applications, and a clock.">
 <legend>Screenshot of a KDE desktop.</legend>
</figure>

A photo on a photo-sharing site, if the site received the image with no metadata other than the caption:

<figure>
 <img src="1100670787_6a7c664aef.jpg">
 <legend>Bubbles traveled everywhere with us.</legend>
</figure>

In this case, though, it would be better if a detailed description of the important parts of the image obtained from the user and included on the page.

Sometimes there simply is no text that can do justice to an image. For example, there is little that can be said to usefully describe a Rorschach inkblot test.

<figure>
 <img src="/commons/a/a7/Rorschach1.jpg">
 <legend>A black outline of the first of the ten cards
 in the Rorschach inkblot test.</legend>
</figure>

Note that the following would be a very bad use of alternative text:

<!-- This example is wrong. Do not copy it. -->
<figure>
 <img src="/commons/a/a7/Rorschach1.jpg" alt="A black outline
 of the first of the ten cards in the Rorschach inkblot test.">
 <legend>A black outline of the first of the ten cards
 in the Rorschach inkblot test.</legend>
</figure>

Including the caption in the alternative text like this isn't useful because it effectively duplicates the caption for users who don't have images, taunting them twice yet not helping them any more than if they had only read or heard the caption once.

Since some users cannot use images at all (e.g. because they have a very slow connection, or because they are using a text-only browser, or because they are listening to the page being read out by a hands-free automobile voice Web browser, or simply because they are blind), the alt attribute is only allowed to be omitted when no alternative text is available and none can be made available, e.g. on automated image gallery sites.

An image in an e-mail or document intended for a specific person who is known to be able to view images

When an image is included in a communication (such as an HTML e-mail) aimed at someone who is known to be able to view images, the alt attribute may be omitted. However, even in such cases it is strongly recommended that alternative text be included (as appropriate according to the kind of image involved, as described in the above entries), so that the e-mail is still usable should the user use a mail client that does not support images, or should the e-mail be forwarded on to other users whose abilities might not include easily seeing images.

The img must not be used as a layout tool. In particular, img elements should not be used to display fully transparent images, as they rarely convey meaning and rarely add anything useful to the document.

There has been some suggestion that the longdesc attribute from HTML4, or some other mechanism that is more powerful than alt="", should be included. This has not yet been considered.

User agent requirements: When the alt attribute is present and its value is the empty string, the image supplements the surrounding content. In such cases, the image may be omitted without affecting the meaning of the document.

When the alt attribute is present and its value is not the empty string, the image is a graphical equivalent of the string given in the alt attribute. In such cases, the image may be replaced in the rendering by the string given in the attribute without significantly affecting the meaning of the document.

When the alt attribute is missing, the image represents a key part of the content. Non-visual user agents should apply image analysis heuristics to help the user make sense of the image.

The alt attribute does not represent advisory information. User agents must not present the contents of the alt attribute in the same way as content of the title attribute.

If the src attribute is omitted, the image represents whatever string is given by the element's alt attribute, if any, or nothing, if that attribute is empty or absent.

The src attribute, on setting, must cause the user agent to immediately begin to download the specified resource, unless the user agent cannot support images, or its support for images has been disabled.

The download of the image must delay the load event.

This, unfortunately, can be used to perform a rudimentary port scan of the user's local network (especially in conjunction with scripting, though scripting isn't actually necessary to carry out such an attack). User agents may implement cross-origin access control policies that mitigate this attack.

Once the download has completed, if the image is a valid image, the user agent must fire a load event on the img element (this happens after complete starts returning true). If the download fails or it completes but the image is not a valid or supported image, the user agent must fire an error event on the img element.

The remote server's response metadata (e.g. an HTTP 404 status code, or associated Content-Type headers) must be ignored when determining whether the resource obtained is a valid image or not.

This allows servers to return images with error responses.

User agents must not support non-image resources with the img element.

The usemap attribute, if present, can indicate that the image has an associated image map.

The ismap attribute, when used on an element that is a descendant of an a element with an href attribute, indicates by its presence that the element provides access to a server-side image map. This affects how events are handled on the corresponding a element.

The ismap attribute is a boolean attribute. The attribute must not be specified on an element that does not have an ancestor a element with an href attribute.

The img element supports dimension attributes.

The DOM attributes alt, src, useMap, and isMap each must reflect the respective content attributes of the same name.

The DOM attributes height and width must return the rendered height and width of the image, in CSS pixels, if the image is being rendered, and is being rendered to a visual medium, or 0 otherwise. [CSS21]

The DOM attribute complete must return true if the user agent has downloaded the image specified in the src attribute, and it is a valid image, and false otherwise.

The value of complete can change while a script is executing.

A single image can have different appropriate alternative text depending on the context.

In each of the following cases, the same image is used, yet the alt text is different each time. The image is the coat of arms of the Canton Geneva in Switzerland.

Here it is used as a supplementary icon:

<p>I lived in <img src="carouge.svg" alt=""> Carouge.</p>

Here it is used as an icon representing the town:

<p>Home town: <img src="carouge.svg" alt="Carouge"></p>

Here it is used as part of a text on the town:

<p>Carouge has a coat of arms.</p>
<p><img src="carouge.svg" alt="The coat of arms depicts a lion, sitting in front of a tree."></p>
<p>It is used as decoration all over the town.</p>

Here it is used as a way to support a similar text where the description is given as well as, instead of as an alternative to, the image:

<p>Carouge has a coat of arms.</p>
<p><img src="carouge.svg" alt=""></p>
<p>The coat of arms depicts a lion, sitting in front of a tree.
It is used as decoration all over the town.</p>

Here it is used as part of a story:

<p>He picked up the folder and a piece of paper fell out.</p>
<p><img src="carouge.svg" alt="Shaped like a shield, the paper had a
red background, a green tree, and a yellow lion with its tongue
hanging out and whose tail was shaped like an S."></p>
<p>He stared at the folder. S! The answer he had been looking for all
this time was simply the letter S! How had he not seen that before? It all
came together now. The phone call where Hector had referred to a lion's tail,
the time Marco had stuck his tongue out...</p>

Here are some more examples showing the same picture used in different contexts, with different appropriate alternate texts each time.

<article>
 <h1>My cats</h1>
 <h2>Fluffy</h2>
 <p>Fluffy is my favourite.</p>
 <img src="fluffy.jpg" alt="She likes playing with a ball of yarn.">
 <p>She's just too cute.</p>
 <h2>Miles</h2>
 <p>My other cat, Miles just eats and sleeps.</p>
</article>
<article>
 <h1>Photography</h1>
 <h2>Shooting moving targets indoors</h2>
 <p>The trick here is to know how to anticipate; to know at what speed and
 what distance the subject will pass by.</p>
 <img src="fluffy.jpg" alt="A cat flying by, chasing a ball of yarn, can be
 photographed quite nicely using this technique.">
 <h2>Nature by night</h2>
 <p>To achieve this, you'll need either an extremely sensitive film, or
 immense flash lights.</p>
</article>
<article>
 <h1>About me</h1>
 <h2>My pets</h2>
 <p>I've got a cat named Fluffy and a dog named Miles.</p>
 <img src="fluffy.jpg" alt="Fluffy, my cat, tends to keep itself busy.">
 <p>My dog Miles and I like go on long walks together.</p>
 <h2>music</h2>
 <p>After our walks, having emptied my mind, I like listening to Bach.</p>
</article>
<article>
 <h1>Fluffy and the Yarn</h1>
 <p>Fluffy was a cat who liked to play with yarn. He also liked to jump.</p>
 <aside><img src="fluffy.jpg" alt="" title="Fluffy"></aside>
 <p>He would play in the morning, he would play in the evening.</p>
</article>

3.12.3 The iframe element

Categories
Embedded content.
Contexts in which this element may be used:
Where embedded content is expected.
Content model:
Text that conforms to the requirements given in the prose.
Element-specific attributes:
src
name
sandbox
seamless
width
height
DOM interface:
interface HTMLIFrameElement : HTMLElement {
           attribute DOMString src;
           attribute DOMString name;
           attribute DOMString sandbox;
           attribute boolean seamless;
           attribute long width;
           attribute long height;
};

Objects implementing the HTMLIFrameElement interface must also implement the EmbeddingElement interface defined in the Window Object specification. [WINDOW]

The iframe element introduces a new nested browsing context.

The src attribute, if present, must be a URI (or IRI) to a page that the nested browsing context is to contain. When the browsing context is created, if the attribute is present, the user agent must navigate this browsing context to the given URI, with replacement enabled, and with the iframe element's document's browsing context as the source browsing context. If the user navigates away from this page, the iframe's corresponding Window object will reference new Document objects, but the src attribute will not change.

Whenever the src attribute is set, the nested browsing context must be navigated to the given URI, with the iframe element's document's browsing context as the source browsing context.

If the src attribute is not set when the element is created, the browsing context will remain at the initial about:blank page.

The name attribute, if present, must be a valid browsing context name. When the browsing context is created, if the attribute is present, the browsing context name must be set to the value of this attribute; otherwise, the browsing context name must be set to the empty string.

Whenever the name attribute is set, the nested browsing context's name must be changed to the new value. If the attribute is removed, the browsing context name must be set to the empty string.

When content loads in an iframe, after any load events are fired within the content itself, the user agent must fire a load event at the iframe element. When content fails to load (e.g. due to a network error), then the user agent must fire an error event at the element instead.

When there is an active parser in the iframe, and when anything in the iframe that is delaying the load event in the iframe's browsing context, the iframe must delay the load event.

If, during the handling of the load event, the browsing context in the iframe is again navigated, that will further delay the load event.


The sandbox attribute, when specified, enables a set of extra restrictions on any content hosted by the iframe. Its value must be an unordered set of unique space-separated tokens. The allowed values are allow-same-origin, allow-forms, and allow-scripts.

While the sandbox attribute is specified, the iframe element's nested browsing context, and all the browsing contexts nested within it (either directly or indirectly through other nested browsing contexts) must have the following flags set:

The sandboxed navigation browsing context flag

This flag prevents content from navigating browsing contexts other than the sandboxed browsing context itself (or browsing contexts further nested inside it).

This flag also prevents content from creating new auxiliary browsing contexts, e.g. using the target attribute or the window.open() method.

The sandboxed plugins browsing context flag

This flag prevents content from instantiating plugins, whether using the embed element, the object element, the applet element, or through navigation of a nested browsing context.

The sandboxed annoyances browsing context flag

This flag prevents content from showing notifications outside of the nested browsing context.

The sandboxed origin browsing context flag, unless the sandbox attribute's value, when split on spaces, is found to have the allow-same-origin keyword set

This flag forces content into a unique origin for the purposes of the same-origin policy.

This flag also prevents script from reading the document.cookies DOM attribute.

The allow-same-origin attribute is intended for two cases.

First, it can be used to allow content from the same site to be sandboxed to disable scripting, while still allowing access to the DOM of the sandboxed content.

Second, it can be used to embed content from a third-party site, sandboxed to prevent that site from opening popup windows, etc, without preventing the embedded page from communicating back to its originating site, using the database APIs to store data, etc.

The sandboxed forms browsing context flag, unless the sandbox attribute's value, when split on spaces, is found to have the allow-forms keyword set

This flag blocks form submission.

The sandboxed scripts browsing context flag, unless the sandbox attribute's value, when split on spaces, is found to have the allow-scripts keyword set

This flag blocks script execution.

These flags must not be set unless the conditions listed above define them as being set.

In this example, some completely-unknown, potentially hostile, user-provided HTML content is embedded in a page. Because it is sandboxed, it is treated by the user agent as being from a unique origin, despite the content being served from the same site. Thus it is affected by all the normal cross-site restrictions. In addition, the embedded page has scripting disabled, plugins disabled, forms disabled, and it cannot navigate any frames or windows other than itself (or any frames or windows it itself embeds).

<p>We're not scared of you! Here is your content, unedited:</p>
<iframe sandbox src="getusercontent.cgi?id=12193"></iframe>

Note that cookies are still send to the server in the getusercontent.cgi request, though they are not visible in the document.cookies DOM attribute.

In this example, a gadget from another site is embedded. The gadget has scripting and forms enabled, and the origin sandbox restrictions are lifted, allowing the gadget to communicate with its originating server. The sandbox is still useful, however, as it disables plugins and popups, thus reducing the risk of the user being exposed to malware and other annoyances.

<iframe sandbox="allow-same-origin allow-forms allow-scripts"
        src="http://maps.example.com/embedded.html"></iframe>

The seamless attribute is a boolean attribute. When specified, it indicates that the iframe element's browsing context is to be rendered in a manner that makes it appear to be part of the containing document (seamlessly included in the parent document). Specifically, when the attribute is set on an element and while the browsing context's active document has the same origin as the iframe element's document, or the browsing context's active document's URI has the same origin as the iframe element's document, the following requirements apply:

Parts of the above might get moved into the rendering section at some point.

If the attribute is not specified, or if the origin conditions listed above are not met, then the user agent should render the nested browsing context in a manner that is clearly distinguishable as a separate browsing context, and the seamless browsing context flag must be set to false for that browsing context.

It is important that user agents recheck the above conditions whenever the active document of the nested browsing context of the iframe changes, such that the seamless browsing context flag gets unset if the nested browsing context is navigated to another origin.

In this example, the site's navigation is embedded using a client-side include using an iframe. Any links in the iframe will, in new user agents, be automatically opened in the iframe's parent browsing context; for legacy user agents, the site could also include a base element with a target attribute with the value _parent. Similarly, in new user agents the styles of the parent page will be automatically applied to the contents of the frame, but to support legacy user agents authors might wish to include the styles explicitly.

<nav><iframe seamless src="nav.include.html"></iframe></nav>

The iframe element supports dimension attributes for cases where the embedded content has specific dimensions (e.g. ad units have well-defined dimensions).

An iframe element never has fallback content, as it will always create a nested browsing context, regardless of whether the specified initial contents are successfully used.

Descendants of iframe elements represent nothing. (In legacy user agents that do not support iframe elements, the contents would be parsed as markup that could act as fallback content.)

The content model of iframe elements is text, except that the text must be such that ... anyone have any bright ideas?

The HTML parser treats markup inside iframe elements as text.

The DOM attributes src, name, sandbox, and seamless must reflect the content attributes of the same name.

3.12.4 The embed element

Categories
Embedded content.
Contexts in which this element may be used:
Where embedded content is expected.
Content model:
Empty.
Element-specific attributes:
src
type
width
height
Any other attribute that has no namespace (see prose).
DOM interface:
interface HTMLEmbedElement : HTMLElement {
           attribute DOMString src;
           attribute DOMString type;
           attribute long width;
           attribute long height;
};

Depending on the type of content instantiated by the embed element, the node may also support other interfaces.

The embed element represents an integration point for an external (typically non-HTML) application or interactive content.

The src attribute gives the address of the resource being embedded. The attribute must be present and contain a URI (or IRI).

If the src attribute is missing, then the embed element must be ignored (it represents nothing).

If the sandboxed plugins browsing context flag is set on the browsing context for which the embed element's document is the active document, then the user agent must render the embed element in a manner that conveys that the plugin was disabled. The user agent may offer the user the option to override the sandbox and instantiate the plugin anyway; if the user invokes such an option, the user agent must act as if the sandboxed plugins browsing context flag was not set for the purposes of this element.

Plugins are disabled in sandboxed browsing contexts because they might not honor the restrictions imposed by the sandbox (e.g. they might allow scripting even when scripting in the sandbox is disabled). User agents should convey the danger of overriding the sandbox to the user if an option to do so is provided.

Otherwise, the src attribute is present, and the element is not in a sandboxed browsing context:

When the src attribute is set, user agents are expected to find an appropriate plugin for the specified resource, based on the content's type, and hand that plugin the content of the resource. If the plugin supports a scriptable interface, the HTMLEmbedElement object representing the element should expose that interfaces.

The download of the resource must delay the load event.

The user agent should pass the names and values of all the attributes of the embed element that have no namespace to the plugin used. Any (namespace-less) attribute may be specified on the embed element.

The embed element has no fallback content. If the user agent can't display the specified resource, e.g. because the given type is not supported, then the user agent must use a default plugin for the content. (This default could be as simple as saying "Unsupported Format", of course.)

The type attribute, if present, gives the MIME type of the linked resource. The value must be a valid MIME type, optionally with parameters. [RFC2046]

The type of the content being embedded is defined as follows:

  1. If the element has a type attribute, then the value of the type attribute is the content's type.
  2. Otherwise, if the specified resource has explicit Content-Type metadata, then that is the content's type.
  3. Otherwise, the content has no type and there can be no appropriate plugin for it.

Should we instead say that the content-sniffing used for top-level browsing contexts should apply here?

Should we require the type attribute to match the server information?

We should say that 404s, etc, don't affect whether the resource is used or not. Not sure how to say it here though.

The embed element supports dimension attributes.

The DOM attributes src and type each must reflect the respective content attributes of the same name.

3.12.5 The object element

Categories
Embedded content.
Contexts in which this element may be used:
Where embedded content is expected.
Content model:
Zero or more param elements, then, transparent.
Element-specific attributes:
data
type
name
usemap
width
height
DOM interface:
interface HTMLObjectElement : HTMLElement {
           attribute DOMString data;
           attribute DOMString type;
           attribute DOMString name;
           attribute DOMString useMap;
           attribute long width;
           attribute long height;
};

Objects implementing the HTMLObjectElement interface must also implement the EmbeddingElement interface defined in the Window Object specification. [WINDOW]

Depending on the type of content instantiated by the object element, the node may also support other interfaces.

The object element can represent an external resource, which, depending on the type of the resource, will either be treated as an image, as a nested browsing context, or as an external resource to be processed by a plugin.

The data attribute, if present, specifies the address of the resource. If present, the attribute must be a URI (or IRI).

The type attribute, if present, specifies the type of the resource. If present, the attribute must be a valid MIME type, optionally with parameters. [RFC2046]

One or both of the data and type attributes must be present.

The name attribute, if present, must be a valid browsing context name.

When the element is created, and subsequently whenever the classid attribute changes, or, if the classid attribute is not present, whenever the data attribute changes, or, if neither classid attribute nor the data attribute are present, whenever the type attribute changes, the user agent must run the following steps to determine what the object element represents:

  1. If the classid attribute is present, and has a value that isn't the empty string, then: if the user agent can find a plugin suitable according to the value of the classid attribute, and plugins aren't being sandboxed, then that plugin should be used, and the value of the data attribute, if any, should be passed to the plugin. If no suitable plugin can be found, or if the plugin reports an error, jump to the last step in the overall set of steps (fallback).

  2. If the data attribute is present, then:

    1. If the type attribute is present and its value is not a type that the user agent supports, and is not a type that the user agent can find a plugin for, then the user agent may jump to the last step in the overall set of steps (fallback) without downloading the content to examine its real type.

    2. Begin a load for the resource.

      The download of the resource must delay the load event.

    3. If the resource is not yet available (e.g. because the resource was not available in the cache, so that loading the resource required making a request over the network), then jump to the last step in the overall set of steps (fallback). When the resource becomes available, or if the load fails, restart this algorithm from this step. Resources can load incrementally; user agents may opt to consider a resource "available" whenever enough data has been obtained to begin processing the resource.

    4. If the load failed (e.g. an HTTP 404 error, a DNS error), fire an error event at the element, then jump to the last step in the overall set of steps (fallback).

    5. Determine the resource type, as follows:

      1. Let the resource type be unknown.

      2. If the resource has associated Content-Type metadata, then let the resource type be the type specified in the resource's Content-Type metadata.

      3. If the resource type is unknown or "application/octet-stream" and there is a type attribute present on the object element, then change the resource type to instead be the type specified in that type attribute.

      4. If the resource type is still unknown, then change the resource type to instead be the sniffed type of the resource.

    6. Handle the content as given by the first of the following cases that matches:

      If the resource type can be handled by a plugin and plugins aren't being sandboxed

      The user agent should use that plugin and pass the content of the resource to that plugin. If the plugin reports an error, then jump to the last step in the overall set of steps (fallback).

      If the resource type is an XML MIME type
      If the resource type is HTML
      If the resource type does not start with "image/"

      The object element must be associated with a nested browsing context, if it does not already have one. The element's nested browsing context must then be navigated to the given resource, with replacement enabled, and with the object element's document's browsing context as the source browsing context. (The data attribute of the object element doesn't get updated if the browsing context gets further navigated to other locations.)

      If the name attribute is present, the browsing context name must be set to the value of this attribute; otherwise, the browsing context name must be set to the empty string.

      navigation might end up treating it as something else, because it can do sniffing. how should we handle that?

      If the resource type starts with "image/", and support for images has not been disabled

      Apply the image sniffing rules to determine the type of the image.

      The object element represents the specified image. The image is not a nested browsing context.

      If the image cannot be rendered, e.g. because it is malformed or in an unsupported format, jump to the last step in the overall set of steps (fallback).

      Otherwise

      The given resource type is not supported. Jump to the last step in the overall set of steps (fallback).

    7. The element's contents are not part of what the object element represents.

    8. Once the resource is completely loaded, fire a load event at the element.

  3. If the data attribute is absent but the type attribute is present, plugins aren't being sandboxed, and the user agent can find a plugin suitable according to the value of the type attribute, then that plugin should be used. If no suitable plugin can be found, or if the plugin reports an error, jump to the next step (fallback).

  4. (Fallback.) The object element represents what the element's contents represent, ignoring any leading param element children. This is the element's fallback content.

When the algorithm above instantiates a plugin, the user agent should pass the names and values of all the parameters given by param elements that are children of the object element to the plugin used. If the plugin supports a scriptable interface, the HTMLObjectElement object representing the element should expose that interface. The plugin is not a nested browsing context.

If the sandboxed plugins browsing context flag is set on the browsing context for which the object element's document is the active document, then the steps above must always act as if they had failed to find a plugin, even if one would otherwise have been used.

Due to the algorithm above, the contents of object elements act as fallback content, used only when referenced resources can't be shown (e.g. because it returned a 404 error). This allows multiple object elements to be nested inside each other, targeting multiple user agents with different capabilities, with the user agent picking the first one it supports.

Whenever the name attribute is set, if the object element has a nested browsing context, its name must be changed to the new value. If the attribute is removed, if the object element has a browsing context, the browsing context name must be set to the empty string.

The usemap attribute, if present while the object element represents an image, can indicate that the object has an associated image map. The attribute must be ignored if the object element doesn't represent an image.

The object element supports dimension attributes.

The DOM attributes data, type, name, and useMap each must reflect the respective content attributes of the same name.

In the following example, a Java applet is embedded in a page using the object element. (Generally speaking, it is better to avoid using applets like these and instead use native JavaScript and HTML to provide the functionality, since that way the application will work on all Web browsers without requiring a third-party plugin. Many devices, especially embedded devices, do not support third-party technologies like Java.)

<figure>
 <object type="application/x-java-applet">
  <param name="code" value="MyJavaClass">
  <p>You do not have Java available, or it is disabled.</p>
 </object>
 <legend>My Java Clock</legend>
</figure>

In this example, an HTML page is embedded in another using the object element.

<figure>
 <object data="clock.html"></object>
 <legend>My HTML Clock</legend>
</figure>

3.12.6 The param element

Categories
None.
Contexts in which this element may be used:
As a child of an object element, before any flow content.
Content model:
Empty.
Element-specific attributes:
name
value
DOM interface:
interface HTMLParamElement : HTMLElement {
           attribute DOMString name;
           attribute DOMString value;
};

The param element defines parameters for plugins invoked by object elements.

The name attribute gives the name of the parameter.

The value attribute gives the value of the parameter.

Both attributes must be present. They may have any value.

If both attributes are present, and if the parent element of the param is an object element, then the element defines a parameter with the given name/value pair.

The DOM attributes name and value must both reflect the respective content attributes of the same name.

3.12.7 The video element

Categories
Embedded content.
Contexts in which this element may be used:
Where embedded content is expected.
Content model:
If the element has a src attribute: transparent.
If the element does not have a src attribute: one or more source elements, then, transparent.
Element-specific attributes:
src
poster
autoplay
start
loopstart
loopend
end
playcount
controls
width
height
DOM interface:
interface HTMLVideoElement : HTMLMediaElement {
           attribute long width;
           attribute long height;
  readonly attribute unsigned long videoWidth;
  readonly attribute unsigned long videoHeight;
           attribute DOMString poster;
};

A video element represents a video or movie.

Content may be provided inside the video element. User agents should not show this content to the user; it is intended for older Web browsers which do not support video, so that legacy video plugins can be tried, or to show text to the users of these older browser informing them of how to access the video contents.

In particular, this content is not fallback content intended to address accessibility concerns. To make video content accessible to the blind, deaf, and those with other physical or cognitive disabilities, authors are expected to provide alternative media streams and/or to embed accessibility aids (such as caption or subtitle tracks) into their media streams.

The video element is a media element whose media data is ostensibly video data, possibly with associated audio data.

The src, autoplay, start, loopstart, loopend, end, playcount, and controls attributes are the attributes common to all media elements.

The video element supports dimension attributes.

The poster attribute gives the address of an image file that the user agent can show while no video data is available. The attribute, if present, must contain a URI (or IRI).

The poster DOM attribute must reflect the poster content attribute.

The videoWidth DOM attribute must return the native width of the video in CSS pixels. The videoHeight DOM attribute must return the native height of the video in CSS pixels. In the absence of resolution information defining the mapping of pixels in the video to physical dimensions, user agents may assume that one pixel in the video corresponds to one CSS pixel. If no video data is available, then the attributes must return 0.

When no video data is available (the element's networkState attribute is either EMPTY, LOADING, or LOADED_METADATA), video elements represent either the image given by the poster attribute, or nothing.

When a video element is actively playing, it represents the frame of video at the continuously increasing "current" position. When the current playback position changes such that the last frame rendered is no longer the frame corresponding to the current playback position in the video, the new frame must be rendered. Similarly, any audio associated with the video must, if played, be played synchronized with the current playback position, at the specified volume with the specified mute state.

When a video element is paused and the current playback position is the first frame of video, the element represents either the frame of video corresponding to the current playback position or the image given by the poster attribute, at the discretion of the user agent.

When a video element is paused at any other position, the element represents the frame of video corresponding to the current playback position, or, if that is not yet available (e.g. because the video is seeking or buffering), the last frame of the video to have been rendered.

When a video element is neither actively playing nor paused (e.g. when seeking or stalled), the element represents the last frame of the video to have been rendered.

Which frame in a video stream corresponds to a particular playback position is defined by the video stream's format.

Video content should be rendered inside the element's playback area such that the video content is shown centered in the playback area at the largest possible size that fits completely within it, with the video content's adjusted aspect ratio being preserved. Thus, if the aspect ratio of the playback area does not match the adjusted aspect ratio of the video, the video will be shown letterboxed. Areas of the element's playback area that do not contain the video represent nothing.

The adjusted aspect ratio of a video is the ratio of its adjusted width to its intrinsic height. The adjusted width of a video is its intrinsic width multiplied by its pixel ratio.

In addition to the above, the user agent may provide messages to the user (such as "buffering", "no video loaded", "error", or more detailed information) by overlaying text or icons on the video or other areas of the element's playback area, or in another appropriate manner.

User agents that cannot render the video may instead make the element represent a link to an external video playback utility or to the video data itself.

User agents should provide controls to enable or disable the display of closed captions associated with the video stream, though such features should, again, not interfere with the page's normal rendering.

User agents may allow users to view the video content in manners more suitable to the user (e.g. full-screen or in an independent resizable window). As for the other user interface features, controls to enable this should not interfere with the page's normal rendering unless the user agent is exposing a user interface. In such an independent context, however, user agents may make full user interfaces visible, with, e.g., play, pause, seeking, and volume controls, even if the controls attribute is absent.

User agents may allow video playback to affect system features that could interfere with the user's experience; for example, user agents could disable screensavers while video playback is in progress.

User agents should not provide a public API to cause videos to be shown full-screen. A script, combined with a carefully crafted video file, could trick the user into thinking a system-modal dialog had been shown, and prompt the user for a password. There is also the danger of "mere" annoyance, with pages launching full-screen videos when links are clicked or pages navigated. Instead, user-agent specific interface features may be provided to easily allow the user to obtain a full-screen playback mode.

The spec does not currently define the interaction of the "controls" attribute with the "height" and "width" attributes. This will likely be defined in the rendering section based on implementation experience. So far, browsers seem to be making the controls overlay-only, thus somewhat sidestepping the issue.

3.12.7.1. Video and audio codecs for video elements

User agents may support any video and audio codecs and container formats.

It would be helpful for interoperability if all browsers could support the same codecs. However, there are no known codecs that satisfy all the current players: we need a codec that is known to not require per-unit or per-distributor licensing, that is compatible with the open source development model, that is of sufficient quality as to be usable, and that is not an additional submarine patent risk for large companies. This is an ongoing issue and this section will be updated once more information is available.

Certain user agents might support no codecs at all, e.g. text browsers running over SSH connections.

3.12.8 The audio element

Categories
Embedded content.
Contexts in which this element may be used:
Where embedded content is expected.
Content model:
If the element has a src attribute: transparent.
If the element does not have a src attribute: one or more source elements, then, transparent.
Element-specific attributes:
src
autoplay
start
loopstart
loopend
end
playcount
controls
DOM interface:
interface HTMLAudioElement : HTMLMediaElement {
  // no members
};

An audio element represents a sound or audio stream.

Content may be provided inside the audio element. User agents should not show this content to the user; it is intended for older Web browsers which do not support audio, so that legacy audio plugins can be tried, or to show text to the users of these older browser informing them of how to access the audio contents.

In particular, this content is not fallback content intended to address accessibility concerns. To make audio content accessible to the deaf or to those with other physical or cognitive disabilities, authors are expected to provide alternative media streams and/or to embed accessibility aids (such as transcriptions) into their media streams.

The audio element is a media element whose media data is ostensibly audio data.

The src, autoplay, start, loopstart, loopend, end, playcount, and controls attributes are the attributes common to all media elements.

When an audio element is actively playing, it must have its audio data played synchronized with the current playback position, at the specified volume with the specified mute state.

When an audio element is not actively playing, audio must not play for the element.

3.12.8.1. Audio codecs for audio elements

User agents may support any audio codecs and container formats.

User agents must support the WAVE container format with audio encoded using the PCM format.

3.12.9 The source element

Categories
None.
Contexts in which this element may be used:
As a child of a media element, before any flow content.
Content model:
Empty.
Element-specific attributes:
src
type
media
pixelratio
DOM interface:
interface HTMLSourceElement : HTMLElement {
           attribute DOMString src;
           attribute DOMString type;
           attribute DOMString media;
           attribute float pixelRatio;
};

The source element allows authors to specify multiple media resources for media elements.

The src attribute gives the address of the media resource. The value must be a URI (or IRI). This attribute must be present.

The type attribute gives the type of the media resource, to help the user agent determine if it can play this media resource before downloading it. Its value must be a MIME type. The codecs parameter may be specified and might be necessary to specify exactly how the resource is encoded. [RFC2046] [RFC4281]

The following list shows some examples of how to use the codecs= MIME parameter in the type attribute.

H.264 Simple baseline profile video (main and extended video compatible) level 3 and Low-Complexity AAC audio in MP4 container
<source src="video.mp4" type="video/mp4; codecs=&quot;avc1.42E01E, mp4a.40.2&quot;">
H.264 Extended profile video (baseline-compatible) level 3 and Low-Complexity AAC audio in MP4 container
<source src="video.mp4" type="video/mp4; codecs=&quot;avc1.58A01E, mp4a.40.2&quot;">
H.264 Main profile video level 3 and Low-Complexity AAC audio in MP4 container
<source src="video.mp4" type="video/mp4; codecs=&quot;avc1.4D401E, mp4a.40.2&quot;">
H.264 "High" profile video (incompatible with main, baseline, or extended profiles) level 3 and Low-Complexity AAC audio in MP4 container
<source src="video.mp4" type="video/mp4; codecs=&quot;avc1.64001E, mp4a.40.2&quot;">
MPEG-4 Visual Simple Profile Level 0 video and Low-Complexity AAC audio in MP4 container
<source src="video.mp4" type="video/mp4; codecs=&quot;mp4v.20.8, mp4a.40.2&quot;">
MPEG-4 Advanced Simple Profile Level 0 video and Low-Complexity AAC audio in MP4 container
<source src="video.mp4" type="video/mp4; codecs=&quot;mp4v.20.240, mp4a.40.2&quot;">
MPEG-4 Visual Simple Profile Level 0 video and AMR audio in 3GPP container
<source src="video.3gp" type="video/3gpp; codecs=&quot;mp4v.20.8, samr&quot;">
Theora video and Vorbis audio in Ogg container
<source src="video.ogv" type="video/ogg; codecs=&quot;theora, vorbis&quot;">
Theora video and Speex audio in Ogg container
<source src="video.ogv" type="video/ogg; codecs=&quot;theora, speex&quot;">
Vorbis audio alone in Ogg container
<source src="audio.ogg" type="audio/ogg; codecs=vorbis">
Speex audio alone in Ogg container
<source src="audio.spx" type="audio/ogg; codecs=speex">
FLAC audio alone in Ogg container
<source src="audio.oga" type="audio/ogg; codecs=flac">
Dirac video and Vorbis audio in Ogg container
<source src="video.ogv" type="video/ogg; codecs=&quot;dirac, vorbis&quot;">
Theora video and Vorbis audio in Matroska container
<source src="video.mkv" type="video/x-matroska; codecs=&quot;theora, vorbis&quot;">

The media attribute gives the intended media type of the media resource, to help the user agent determine if this media resource is useful to the user before downloading it. Its value must be a valid media query. [MQ]

Either the type attribute, the media attribute or both, must be specified, unless this is the last source element child of the parent element.

The pixelratio attribute allows the author to specify the pixel ratio of anamorphic media resources that do not self-describe their pixel ratio. The attribute value, if specified, must be a valid floating point number giving the ratio of the correct rendered width of each pixel to the actual width of each pixel in the image (i.e., the multiple by which the video's intrinsic width is to be multiplied to obtain the rendered width that gives the correct aspect ratio). The default value, if the attribute is omitted or cannot be parsed, is 1.0.

If a source element is inserted into a media element that is already in a document and whose networkState is in the EMPTY state, the user agent must implicitly invoke the load() method on the media element as soon as all other scripts have finished executing. Any exceptions raised must be ignored.

The DOM attributes src, type, and media must reflect the respective content attributes of the same name.

The DOM attribute pixelRatio must reflect the pixelratio content attribute.

3.12.10 Media elements

Media elements implement the following interface:

interface HTMLMediaElement : HTMLElement {

  // error state
  readonly attribute MediaError error;

  // network state
           attribute DOMString src;
  readonly attribute DOMString currentSrc;
  const unsigned short EMPTY = 0;
  const unsigned short LOADING = 1;
  const unsigned short LOADED_METADATA = 2;
  const unsigned short LOADED_FIRST_FRAME = 3;
  const unsigned short LOADED = 4;
  readonly attribute unsigned short networkState;
  readonly attribute float bufferingRate;
  readonly attribute boolean bufferingThrottled;
  readonly attribute TimeRanges buffered;
  readonly attribute ByteRanges bufferedBytes;
  readonly attribute unsigned long totalBytes;
  void load();

  // ready state
  const unsigned short DATA_UNAVAILABLE = 0;
  const unsigned short CAN_SHOW_CURRENT_FRAME = 1;
  const unsigned short CAN_PLAY = 2;
  const unsigned short CAN_PLAY_THROUGH = 3;
  readonly attribute unsigned short readyState;
  readonly attribute boolean seeking;

  // playback state
           attribute float currentTime;
  readonly attribute float duration;
  readonly attribute boolean paused;
           attribute float defaultPlaybackRate;
           attribute float playbackRate;
  readonly attribute TimeRanges played;
  readonly attribute TimeRanges seekable;
  readonly attribute boolean ended;
           attribute boolean autoplay;
  void play();
  void pause();

  // looping
           attribute float start;
           attribute float end;
           attribute float loopStart;
           attribute float loopEnd;
           attribute unsigned long playCount;
           attribute unsigned long currentLoop;

  // cue ranges
  void addCueRange(in DOMString className, in float start, in float end, in boolean pauseOnExit, in VoidCallback enterCallback, in VoidCallback exitCallback);
  void removeCueRanges(in DOMString className);

  // controls
           attribute boolean controls;
           attribute float volume;
           attribute boolean muted;
};

The media element attributes, src, autoplay, start, loopstart, loopend, end, playcount, and controls, apply to all media elements. They are defined in this section.

Media elements are used to present audio data, or video and audio data, to the user. This is referred to as media data in this section, since this section applies equally to media elements for audio or for video. The term media resource is used to refer to the complete set of media data, e.g. the complete video file, or complete audio file.

3.12.10.1. Error codes

All media elements have an associated error status, which records the last error the element encountered since the load() method was last invoked. The error attribute, on getting, must return the MediaError object created for this last error, or null if there has not been an error.

interface MediaError {
  const unsigned short MEDIA_ERR_ABORTED = 1;
  const unsigned short MEDIA_ERR_NETWORK = 2;
  const unsigned short MEDIA_ERR_DECODE = 3;
  readonly attribute unsigned short code;
};

The code attribute of a MediaError object must return the code for the error, which must be one of the following:

MEDIA_ERR_ABORTED (numeric value 1)
The download of the media resource was aborted by the user agent at the user's request.
MEDIA_ERR_NETWORK (numeric value 2)
A network error of some description caused the user agent to stop downloading the media resource.
MEDIA_ERR_DECODE (numeric value 3)
An error of some description occurred while decoding the media resource.
3.12.10.2. Location of the media resource

The src content attribute on media elements gives the address of the media resource (video, audio) to show. The attribute, if present, must contain a URI (or IRI).

If the src attribute of a media element that is already in a document and whose networkState is in the EMPTY state is added, changed, or removed, the user agent must implicitly invoke the load() method on the media element as soon as all other scripts have finished executing. Any exceptions raised must be ignored.

If a src attribute is specified, the resource it specifies is the media resource that will be used. Otherwise, the resource specified by the first suitable source element child of the media element is the one used.

The src DOM attribute on media elements must reflect the content attribute of the same name.

To pick a media resource for a media element, a user agent must use the following steps:

  1. Let the chosen resource's pixel ratio be 1.0.

  2. If the media element has a src, then the address given in that attribute is the address of the media resource; jump to the last step.

  3. Otherwise, let candidate be the first source element child in the media element, or null if there is no such child.

  4. Loop: this is the start of the loop that looks at the source elements.

  5. If candidate is not null and it has a pixelratio attribute, then let the chosen resource's pixel ratio be result of applying the rules for parsing floating point number values to the value of that attribute, or 1.0 if those rules return an error.

  6. If either:

    ...then the candidate is not suitable; go to the next step.

    Otherwise, the address given in that candidate element's src attribute is the address of the media resource; jump to the last step.

  7. Let candidate be the next source element child in the media element, or null if there are no more such children.

  8. If candidate is not null, return to the step labeled loop.

  9. There is no media resource. Abort these steps.

  10. Let the address of the chosen media resource be the one that was found before jumping to this step, and let its pixel ratio be the value of the chosen resource's pixel ratio.

The currentSrc DOM attribute must return the empty string if the media element's networkState has the value EMPTY, and the absolute URL of the chosen media resource otherwise.

3.12.10.3. Network states

As media elements interact with the network, they go through several states. The networkState attribute, on getting, must return the current network state of the element, which must be one of the following values:

EMPTY (numeric value 0)
The element has not yet been initialized. All attributes are in their initial states.
LOADING (numeric value 1)
The element has picked a media resource (the chosen media resource is available from the currentSrc attribute), but none of the metadata has yet been obtained and therefore all the other attributes are still in their initial states.
LOADED_METADATA (numeric value 2)
Enough of the resource has been obtained that the metadata attributes are initialized (e.g. the length is known). The API will no longer raise exceptions when used.
LOADED_FIRST_FRAME (numeric value 3)
Actual media data has been obtained. In the case of video, this specifically means that a frame of video is available and can be shown.
LOADED (numeric value 4)
The entire media resource has been obtained and is available to the user agent locally. Network connectivity could be lost without affecting the media playback.

The algorithm for the load() method defined below describes exactly when the networkState attribute changes value.

3.12.10.4. Loading the media resource

All media elements have a begun flag, which must begin in the false state, a loaded-first-frame flag, which must begin in the false state, and an autoplaying flag, which must begin in the true state.

When the load() method on a media element is invoked, the user agent must run the following steps. Note that this algorithm might get aborted, e.g. if the load() method itself is invoked again.

  1. Any already-running instance of this algorithm for this element must be aborted. If those method calls have not yet returned, they must finish the step they are on, and then immediately return.

  2. If the element's begun flag is true, then the begun flag must be set to false, the error attribute must be set to a new MediaError object whose code attribute is set to MEDIA_ERR_ABORTED, and the user agent must synchronously fire a progress event called abort at the media element.

  3. The error attribute must be set to null, the loaded-first-frame flag must be set to false, and the autoplaying flag must be set to true.

  4. The playbackRate attribute must be set to the value of the defaultPlaybackRate attribute.

  5. If the media element's networkState is not set to EMPTY, then the following substeps must be followed:

    1. The networkState attribute must be set to EMPTY.
    2. If readyState is not set to DATA_UNAVAILABLE, it must be set to that state.
    3. If the paused attribute is false, it must be set to true.
    4. If seeking is true, it must be set to false.
    5. The current playback position must be set to 0.
    6. The currentLoop DOM attribute must be set to 0.
    7. The user agent must synchronously fire a simple event called emptied at the media element.
  6. The user agent must pick a media resource for the media element. If that fails, the method must raise an INVALID_STATE_ERR exception, and abort these steps.

  7. The networkState attribute must be set to LOADING.

  8. The currentSrc attribute starts returning the new value.

  9. The user agent must then set the begun flag to true and fire a progress event called loadstart at the media element.

  10. The method must return, but these steps must continue.

  11. Playback of any previously playing media resource for this element stops.

  12. If a download is in progress for the media element, the user agent should stop the download.

  13. The user agent must then begin to download the chosen media resource. The rate of the download may be throttled, however, in response to user preferences (including throttling it to zero until the user indicates that the download can start), or to balance the download with other connections sharing the same bandwidth.

  14. While the download is progressing, the user agent must fire a progress event called progress at the element every 350ms (±200ms) or for every byte received, whichever is least frequent.

    If at any point the user agent has received no data for more than about three seconds, the user agent must fire a progress event called stalled at the element.

    User agents may allow users to selectively block or slow media data downloads. When a media element's download has been blocked, the user agent must act as if it was stalled (as opposed to acting as if the connection was closed).

    The user agent may use whatever means necessary to download the resource (within the constraints put forward by this and other specifications); for example, reconnecting to the server in the face of network errors, using HTTP partial range requests, or switching to a streaming protocol. The user agent must consider a resource erroneous only if it has given up trying to download it.

    If the media data cannot be downloaded at all, due to network errors, causing the user agent to give up trying to download the resource

    DNS errors and HTTP 4xx and 5xx errors (and equivalents in other protocols) must cause the user agent to execute the following steps. User agents may also follow these steps in response to other network errors of similar severity.

    1. The user agent should cancel the download.
    2. The error attribute must be set to a new MediaError object whose code attribute is set to MEDIA_ERR_NETWORK.
    3. The begun flag must be set to false and the user agent must fire a progress event called error at the media element.
    4. The element's networkState attribute must be switched to the EMPTY value and the user agent must fire a simple event called emptied at the element.
    5. These steps must be aborted.
    If the media data can be downloaded but is in an unsupported format, or can otherwise not be rendered at all

    The server returning a file of the wrong kind (e.g. one that that turns out to not be pure audio when the media element is an audio element), or the file using unsupported codecs for all the data, must cause the user agent to execute the following steps. User agents may also execute these steps in response to other codec-related fatal errors, such as the file requiring more resources to process than the user agent can provide in real time.

    1. The user agent should cancel the download.
    2. The error attribute must be set to a new MediaError object whose code attribute is set to MEDIA_ERR_DECODE.
    3. The begun flag must be set to false and the user agent must fire a progress event called error at the media element.
    4. The element's networkState attribute must be switched to the EMPTY value and the user agent must fire a simple event called emptied at the element.
    5. These steps must be aborted.
    If the media data download is aborted by the user

    The download is aborted by the user, e.g. because the user navigated the browsing context to another page, the user agent must execute the following steps. These steps are not followed if the load() method itself is reinvoked, as the steps above handle that particular kind of abort.

    1. The user agent should cancel the download.
    2. The error attribute must be set to a new MediaError object whose code attribute is set to MEDIA_ERR_ABORT.
    3. The begun flag must be set to false and the user agent must fire a progress event called abort at the media element.
    4. If the media element's networkState attribute has the value LOADING, the element's networkState attribute must be switched to the EMPTY value and the user agent must fire a simple event called emptied at the element. (If the networkState attribute has a value greater than LOADING, then this doesn't happen; the available data, if any, will be playable.)
    5. These steps must be aborted.
    If the media data can be downloaded but has non-fatal errors or uses, in part, codecs that are unsupported, preventing the user agent from rendering the content completely correctly but not preventing playback altogether

    The server returning data that is partially usable but cannot be optimally rendered must cause the user agent to execute the following steps.

    1. Should we fire a 'warning' event? Set the 'error' flag to 'MEDIA_ERR_SUBOPTIMAL' or something?
    Once enough of the media data has been downloaded to determine the duration of the media resource, its dimensions, and other metadata

    The user agent must follow these substeps:

    1. The current playback position must be set to the effective start.

    2. The networkState attribute must be set to LOADED_METADATA.

    3. A number of attributes, including duration, buffered, and played, become available.

    4. The user agent will fire a simple event called durationchange at the element at this point.

    5. The user agent must fire a simple event called loadedmetadata at the element.

    Once enough of the media data has been downloaded to enable the user agent to display the frame at the effective start of the media resource

    The user agent must follow these substeps:

    1. The networkState attribute must be set to LOADED_FIRST_FRAME.

    2. The readyState attribute must change to CAN_SHOW_CURRENT_FRAME.

    3. The loaded-first-frame flag must be set to true.

    4. The user agent must fire a simple event called loadedfirstframe at the element.

    5. The user agent must fire a simple event called canshowcurrentframe at the element.

    When the user agent has completed the download of the entire media resource, it must move on to the next step.

  15. If the download completes without errors, the begun flag must be set to false, the networkState attribute must be set to LOADED, and the user agent must fire a progress event called load at the element.

If a media element whose networkState has the value EMPTY is inserted into a document, user agents must implicitly invoke the load() method on the media element as soon as all other scripts have finished executing. Any exceptions raised must be ignored.

The bufferingRate attribute must return the average number of bits received per second for the current download over the past few seconds. If there is no download in progress, the attribute must return 0.

The bufferingThrottled attribute must return true if the user agent is intentionally throttling the bandwidth used by the download (including when throttling to zero to pause the download altogether), and false otherwise.

The buffered attribute must return a static normalized TimeRanges object that represents the ranges of the media resource, if any, that the user agent has downloaded, at the time the attribute is evaluated.

Typically this will be a single range anchored at the zero point, but if, e.g. the user agent uses HTTP range requests in response to seeking, then there could be multiple ranges.

The bufferedBytes attribute must return a static normalized ByteRanges object that represents the ranges of the media resource, if any, that the user agent has downloaded, at the time the attribute is evaluated.

The totalBytes attribute must return the length of the media resource, in bytes, if it is known and finite. If it is not known, is infinite (e.g. streaming radio), or if no media data is available, the attribute must return 0.

3.12.10.5. Offsets into the media resource

The duration attribute must return the length of the media resource, in seconds. If no media data is available, then the attributes must return 0. If media data is available but the length is not known, the attribute must return the Not-a-Number (NaN) value. If the media resource is known to be unbounded (e.g. a streaming radio), then the attribute must return the positive Infinity value.

When the length of the media resource changes (e.g. from being unknown to known, or from indeterminate to known, or from a previously established length to a new length) the user agent must, once any running scripts have finished, fire a simple event called durationchange at the media element.

Media elements have a current playback position, which must initially be zero. The current position is a time.

The currentTime attribute must, on getting, return the current playback position, expressed in seconds. On setting, the user agent must seek to the new value (which might raise an exception).

The start content attribute gives the offset into the media resource at which playback is to begin. The default value is the default start position of the media resource, or 0 if not enough media data has been obtained yet to determine the default start position or if the resource doesn't specify a default start position.

The effective start is the smaller of the start DOM attribute and the end of the media resource.

The loopstart content attribute gives the offset into the media resource at which playback is to begin when looping a clip. The default value of the loopstart content attribute is the value of the start DOM attribute.

The effective loop start is the smaller of the loopStart DOM attribute and the end of the media resource.

The loopend content attribute gives an offset into the media resource at which playback is to jump back to the loopstart, when looping the clip. The default value of the loopend content attribute is the value of the end DOM attribute.

The effective loop end is the greater of the start, loopStart, and loopEnd DOM attributes, except if that is greater than the end of the media resource, in which case that's its value.

The end content attribute gives an offset into the media resource at which playback is to end. The default value is infinity.

The effective end is the greater of the start, loopStart, and end DOM attributes, except if that is greater than the end of the media resource, in which case that's its value.

The start, loopstart, loopend, and end attributes must, if specified, contain value time offsets. To get the time values they represent, user agents must use the rules for parsing time offsets.

The start, loopStart, loopEnd, and end DOM attributes must reflect the start, loopstart, loopend, and end content attributes on the media element respectively.

The playcount content attribute gives the number of times to play the clip. The default value is 1.

The playCount DOM attribute must reflect the playcount content attribute on the media element. The value must be limited to only positive non-zero numbers.

The currentLoop attribute must initially have the value 0. It gives the index of the current loop. It is changed during playback as described below.

When any of the start, loopStart, loopEnd, end, and playCount DOM attributes change value (either through content attribute mutations reflecting into the DOM attribute, or direct mutations of the DOM attribute), the user agent must apply the following steps:

  1. If the playCount DOM attribute's value is less than or equal to the currentLoop DOM attribute's value, then the currentLoop DOM attribute's value must be set to playCount-1 (which will make the current loop the last loop).

  2. If the media element's networkState is in the EMPTY state or the LOADING state, then the user agent must at this point abort these steps.

  3. If the currentLoop is zero, and the current playback position is before the effective start, the user agent must seek to the effective start.

  4. If the currentLoop is greater than zero, and the current playback position is before the effective loop start, the user agent must seek to the effective loop start.

  5. If the currentLoop is less than playCount-1, and the current playback position is after the effective loop end, the user agent must seek to the effective loop start, and increase currentLoop by 1.

  6. If the currentLoop is equal to playCount-1, and the current playback position is after the effective end, the user agent must seek to the effective end and then the looping will end.

3.12.10.6. The ready states

Media elements have a ready state, which describes to what degree they are ready to be rendered at the current playback position. The possible values are as follows; the ready state of a media element at any particular time is the greatest value describing the state of the element:

DATA_UNAVAILABLE (numeric value 0)
No data for the current playback position is available. Media elements whose networkState attribute is less than LOADED_FIRST_FRAME are always in the DATA_UNAVAILABLE state.
CAN_SHOW_CURRENT_FRAME (numeric value 1)
Data for the immediate current playback position is available, but not enough data is available that the user agent could successfully advance the current playback position at all without immediately reverting to the DATA_UNAVAILABLE state. In video, this corresponds to the user agent having data from the current frame, but not the next frame. In audio, this corresponds to the user agent only having audio up to the current playback position, but no further.
CAN_PLAY (numeric value 2)
Data for the immediate current playback position is available, as well as enough data for the user agent to advance the current playback position at least a little without immediately reverting to the DATA_UNAVAILABLE state. In video, this corresponds to the user agent having data for the current frame and the next frame. In audio, this corresponds to the user agent having data beyond the current playback position.
CAN_PLAY_THROUGH (numeric value 3)
Data for the immediate current playback position is available, as well as enough data for the user agent to advance the current playback position at least a little without immediately reverting to the DATA_UNAVAILABLE state, and, in addition, the user agent estimates that data is being downloaded at a rate where the current playback position, if it were to advance at the rate given by the defaultPlaybackRate attribute, would not overtake the available data before playback reaches the effective end of the media resource on the last loop.

When the ready state of a media element whose networkState is not EMPTY changes, the user agent must follow the steps given below:

If the new ready state is DATA_UNAVAILABLE

The user agent must fire a simple event called dataunavailable at the element.

If the new ready state is CAN_SHOW_CURRENT_FRAME

If the element's loaded-first-frame flag is true, the user agent must fire a simple event called canshowcurrentframe event.

The first time the networkState attribute switches to this value, the loaded-first-frame flag is false, and the event is fired by the algorithm described above for the load() method, in conjunction with other steps.

If the new ready state is CAN_PLAY

The user agent must fire a simple event called canplay.

If the new ready state is CAN_PLAY_THROUGH

The user agent must fire a simple event called canplaythrough event. If the autoplaying flag is true, and the paused attribute is true, and the media element has an autoplay attribute specified, then the user agent must also set the paused attribute to false and fire a simple event called play.

It is possible for the ready state of a media element to jump between these states discontinuously. For example, the state of a media element whose leaded-first-frame flag is false can jump straight from DATA_UNAVAILABLE to CAN_PLAY_THROUGH without passing through the CAN_SHOW_CURRENT_FRAME and CAN_PLAY states, and thus without firing the canshowcurrentframe and canplay events. The only state that is guaranteed to be reached is the CAN_SHOW_CURRENT_FRAME state, which is reached as part of the load() method's processing.

The readyState DOM attribute must, on getting, return the value described above that describes the current ready state of the media element.

The autoplay attribute is a boolean attribute. When present, the algorithm described herein will cause the user agent to automatically begin playback of the media resource as soon as it can do so without stopping.

The autoplay DOM attribute must reflect the content attribute of the same name.

3.12.10.7. Playing the media resource

The paused attribute represents whether the media element is paused or not. The attribute must initially be true.

A media element is said to be actively playing when its paused attribute is false, the readyState attribute is either CAN_PLAY or CAN_PLAY_THROUGH, the element has not ended playback, playback has not stopped due to errors, and the element has not paused for user interaction.

A media element is said to have ended playback when the element's networkState attribute is LOADED_METADATA or greater, the current playback position is equal to the effective end of the media resource, and the currentLoop attribute is equal to playCount-1.

A media element is said to have stopped due to errors when the element's networkState attribute is LOADED_METADATA or greater, and the user agent encounters a non-fatal error during the processing of the media data, and due to that error, is not able to play the content at the current playback position.

A media element is said to have paused for user interaction when its paused attribute is false, the readyState attribute is either CAN_PLAY or CAN_PLAY_THROUGH and the user agent has reached a point in the media resource where the user has to make a selection for the resource to continue.

It is possible for a media element to have both ended playback and paused for user interaction at the same time.

When a media element is actively playing and its owner Document is an active document, its current playback position must increase monotonically at playbackRate units of media time per unit time of wall clock time. If this value is not 1, the user agent may apply pitch adjustments to any audio component of the media resource.

Media resources might be internally scripted or interactive. Thus, a media element could play in a non-linear fashion. If this happens, the user agent must act as if the algorithm for seeking was used whenever the current playback position changes in a discontinuous fashion (so that the relevant events fire).

When a media element that is actively playing stops playing because its readyState attribute changes to a value lower than CAN_PLAY, without the element having ended playback, or playback having stopped due to errors, or playback having paused for user interaction, or the seeking algorithm being invoked, the user agent must fire a simple event called timeupdate at the element, and then must fire a simple event called waiting at the element.

When a media element that is actively playing stops playing because it has paused for user interaction, the user agent must fire a simple event called timeupdate at the element.

When currentLoop is less than playCount-1 and the current playback position reaches the effective loop end, then the user agent must seek to the effective loop start, increase currentLoop by 1, and fire a simple event called timeupdate.

When currentLoop is equal to the playCount-1 and the current playback position reaches the effective end, then the user agent must follow these steps:

  1. The user agent must stop playback.

  2. The ended attribute becomes true.

  3. The user agent must fire a simple event called timeupdate at the element.

  4. The user agent must fire a simple event called ended at the element.

The defaultPlaybackRate attribute gives the desired speed at which the media resource is to play, as a multiple of its intrinsic speed. The attribute is mutable, but on setting, if the new value is 0.0, a NOT_SUPPORTED_ERR exception must be raised instead of the value being changed. It must initially have the value 1.0.

The playbackRate attribute gives the speed at which the media resource plays, as a multiple of its intrinsic speed. If it is not equal to the defaultPlaybackRate, then the implication is that the user is using a feature such as fast forward or slow motion playback. The attribute is mutable, but on setting, if the new value is 0.0, a NOT_SUPPORTED_ERR exception must be raised instead of the value being changed. Otherwise, the playback must change speed (if the element is actively playing). It must initially have the value 1.0.

When the defaultPlaybackRate or playbackRate attributes change value (either by being set by script or by being changed directly by the user agent, e.g. in response to user control) the user agent must, once any running scripts have finished, fire a simple event called ratechange at the media element.

When the play() method on a media element is invoked, the user agent must run the following steps.

  1. If the media element's networkState attribute has the value EMPTY, then the user agent must invoke the load() method and wait for it to return. If that raises an exception, that exception must be reraised by the play() method.

  2. If the playback has ended, then the user agent must set currentLoop to zero and seek to the effective start.

    If this involved a seek, the user agent will fire a simple event called timeupdate at the media element.

  3. The playbackRate attribute must be set to the value of the defaultPlaybackRate attribute.

    If this caused the playbackRate attribute to change value, the user agent will fire a simple event called ratechange at the media element.

  4. If the media element's paused attribute is true, it must be set to false.

  5. The media element's autoplaying flag must be set to false.

  6. The method must then return.

  7. If the fourth step above changed the value of paused, the user agent must, after any running scripts have finished executing, and after any other events triggered by this algorithm (specifically timeupdate and ratechange) have fired, fire a simple event called play at the element.

When the pause() method is invoked, the user agent must run the following steps:

  1. If the media element's networkState attribute has the value EMPTY, then the user agent must invoke the load() method and wait for it to return. If that raises an exception, that exception must be reraised by the pause() method.

  2. If the media element's paused attribute is false, it must be set to true.

  3. The media element's autoplaying flag must be set to false.

  4. The method must then return.

  5. If the second step above changed the value of paused, then, after any running scripts have finished executing, the user agent must first fire a simple event called timeupdate at the element, and then fire a simple event called pause at the element.

When a media element is removed from a Document, if the media element's networkState attribute has a value other than EMPTY then the user agent must act as if the pause() method had been invoked.

Media elements that are actively playing while not in a Document must not play any video, but should play any audio component. Media elements must not stop playing just because all references to them have been removed; only once a media element to which no references exist has reached a point where no further audio remains to be played for that element (e.g. because the element is paused or because the end of the clip has been reached) may the element be garbage collected.

If the media element's ownerDocument stops being an active document, then the playback will stop until the document is active again.

The ended attribute must return true if the media element has ended playback, and false otherwise.

The played attribute must return a static normalized TimeRanges object that represents the ranges of the media resource, if any, that the user agent has so far rendered, at the time the attribute is evaluated.

3.12.10.8. Seeking

The seeking attribute must initially have the value false.

When the user agent is required to seek to a particular new playback position in the media resource, it means that the user agent must run the following steps:

  1. If the media element's networkState is less than LOADED_METADATA, then the user agent must raise an INVALID_STATE_ERR exception (if the seek was in response to a DOM method call or setting of a DOM attribute), and abort these steps.

  2. If currentLoop is 0, let min be the effective start. Otherwise, let it be the effective loop start.

  3. If currentLoop is equal to playCount-1, let max be the effective end. Otherwise, let it be the effective loop end.

  4. If the new playback position is more than max, let it be max.

  5. If the new playback position is less than min, let it be min.

  6. If the (possibly now changed) new playback position is not in one of the ranges given in the seekable attribute, then the user agent must raise an INDEX_SIZE_ERR exception (if the seek was in response to a DOM method call or setting of a DOM attribute), and abort these steps.

  7. The current playback position must be set to the given new playback position.

  8. The seeking DOM attribute must be set to true.

  9. If the seek was in response to a DOM method call or setting of a DOM attribute, then continue the script. The remainder of these steps must be run asynchronously.

  10. Once any running scripts have finished executing, the user agent must fire a simple event called timeupdate at the element.

  11. If the media element was actively playing immediately before it started seeking, but seeking caused its readyState attribute to change to a value lower than CAN_PLAY, the user agent must fire a simple event called waiting at the element.

  12. If, when it reaches this step, the user agent has still not established whether or not the media data for the new playback position is available, and, if it is, decoded enough data to play back that position, the user agent must fire a simple event called seeking at the element.

  13. The user agent must wait until it has established whether or not the media data for the new playback position is available, and, if it is, until it has decoded enough data to play back that position.

  14. The seeking DOM attribute must be set to false.

  15. Once any running scripts have finished executing, the user agent must fire a simple event called seeked at the element.

The seekable attribute must return a static normalized TimeRanges object that represents the ranges of the media resource, if any, that the user agent is able to seek to, at the time the attribute is evaluated, notwithstanding the looping attributes (i.e. the effective start and effective end, etc, don't affect the seekable attribute).

If the user agent can seek to anywhere in the media resource, e.g. because it a simple movie file and the user agent and the server support HTTP Range requests, then the attribute would return an object with one range, whose start is the time of the first frame (typically zero), and whose end is the same as the time of the first frame plus the duration attribute's value (which would equal the time of the last frame).

3.12.10.9. Cue ranges

Media elements have a set of cue ranges. Each cue range is made up of the following information:

A class name
A group of related ranges can be given the same class name so that they can all be removed at the same time.
A start time
An end time
The actual time range, using the same timeline as the media resource itself.
A "pause" boolean
A flag indicating whether to pause playback on exit.
An "enter" callback
A callback that is called when the current playback position enters the range.
An "exit" callback
A callback that is called when the current playback position exits the range.
An "active" boolean
A flag indicating whether the range is active or not.

The addCueRange(className, start, end, pauseOnExit, enterCallback, exitCallback) method must, when called, add a cue range to the media element, that cue range having the class name className, the start time start (in seconds), the end time end (in seconds), the "pause" boolean with the same value as pauseOnExit, the "enter" callback enterCallback, the "exit" callback exitCallback, and an "active" boolean that is true if the current playback position is equal to or greater than the start time and less than the end time, and false otherwise.

The removeCueRanges(className) method must, when called, remove all the cue ranges of the media element which have the class name className.

When the current playback position of a media element changes (e.g. due to playback or seeking), the user agent must run the following steps. If the current playback position changes while the steps are running, then the user agent must wait for the steps to complete, and then must immediately rerun the steps. (These steps are thus run as often as possible or needed — if one iteration takes a long time, this can cause certain ranges to be skipped over as the user agent rushes ahead to "catch up".)

  1. Let current ranges be an ordered list of cue ranges, initialized to contain all the cue ranges of the media element whose start times are less than or equal to the current playback position and whose end times are greater than the current playback position, in the order they were added to the element.

  2. Let other ranges be an ordered list of cue ranges, initialized to contain all the cue ranges of the media element that are not present in current ranges, in the order they were added to the element.

  3. If none of the cue ranges in current ranges have their "active" boolean set to "false" (inactive) and none of the cue ranges in other ranges have their "active" boolean set to "true" (active), then abort these steps.

  4. If the time was reached through the usual monotonic increase of the current playback position during normal playback, the user agent must then fire a simple event called timeupdate at the element. (In the other cases, such as explicit seeks, relevant events get fired as part of the overall process of changing the current playback position.)

  5. If the time was reached through the usual monotonic increase of the current playback position during normal playback, and there are cue ranges in other ranges that have both their "active" boolean and their "pause" boolean set to "true", then immediately act as if the element's pause() method had been invoked. (In the other cases, such as explicit seeks, playback is not paused by exiting a cue range, even if that cue range has its "pause" boolean set to "true".)

  6. Invoke all the non-null "exit" callbacks for all of the cue ranges in other ranges that have their "active" boolean set to "true" (active), in list order.

  7. Invoke all the non-null "enter" callbacks for all of the cue ranges in current ranges that have their "active" boolean set to "false" (inactive), in list order.

  8. Set the "active" boolean of all the cue ranges in the current ranges list to "true" (active), and the "active" boolean of all the cue ranges in the other ranges list to "false" (inactive).

Invoking a callback (an object implementing the VoidCallback interface) means calling its handleEvent() method.

interface VoidCallback {
  void handleEvent();
};

The handleEvent method of objects implementing the VoidCallback interface is the entry point for the callback represented by the object.

3.12.10.10. User interface

The controls attribute is a boolean attribute. If the attribute is present, or if the media element is without script, then the user agent should expose a user interface to the user. This user interface should include features to begin playback, pause playback, seek to an arbitrary position in the content (if the content supports arbitrary seeking), change the volume, and show the media content in manners more suitable to the user (e.g. full-screen video or in an independent resizable window). Other controls may also be made available.

If the attribute is absent, then the user agent should avoid making a user interface available that could conflict with an author-provided user interface. User agents may make the following features available, however, even when the attribute is absent:

User agents may provide controls to affect playback of the media resource (e.g. play, pause, seeking, and volume controls), but such features should not interfere with the page's normal rendering. For example, such features could be exposed in the media element's context menu.

Where possible (specifically, for starting, stopping, pausing, and unpausing playback, for muting or changing the volume of the audio, and for seeking), user interface features exposed by the user agent must be implemented in terms of the DOM API described above, so that, e.g., all the same events fire.

The controls DOM attribute must reflect the content attribute of the same name.

The volume attribute must return the playback volume of any audio portions of the media element, in the range 0.0 (silent) to 1.0 (loudest). Initially, the volume must be 0.5, but user agents may remember the last set value across sessions, on a per-site basis or otherwise, so the volume may start at other values. On setting, if the new value is in the range 0.0 to 1.0 inclusive, the attribute must be set to the new value and the playback volume must be correspondingly adjusted as soon as possible after setting the attribute, with 0.0 being silent, and 1.0 being the loudest setting, values in between increasing in loudness. The range need not be linear. The loudest setting may be lower than the system's loudest possible setting; for example the user could have set a maximum volume. If the new value is outside the range 0.0 to 1.0 inclusive, then, on setting, an INDEX_SIZE_ERR exception must be raised instead.

The muted attribute must return true if the audio channels are muted and false otherwise. On setting, the attribute must be set to the new value; if the new value is true, audio playback for this media resource must then be muted, and if false, audio playback must then be enabled.

Whenever either the muted or volume attributes are changed, after any running scripts have finished executing, the user agent must fire a simple event called volumechange at the media element.

3.12.10.11. Time ranges

Objects implementing the TimeRanges interface represent a list of ranges (periods) of time.

interface TimeRanges {
  readonly attribute unsigned long length;
  float start(in unsigned long index);
  float end(in unsigned long index);
};

The length DOM attribute must return the number of ranges represented by the object.

The start(index) method must return the position of the start of the indexth range represented by the object, in seconds measured from the start of the timeline that the object covers.

The end(index) method must return the position of the end of the indexth range represented by the object, in seconds measured from the start of the timeline that the object covers.

These methods must raise INDEX_SIZE_ERR exceptions if called with an index argument greater than or equal to the number of ranges represented by the object.

When a TimeRanges object is said to be a normalized TimeRanges object, the ranges it represents must obey the following criteria:

In other words, the ranges in such an object are ordered, don't overlap, aren't empty, and don't touch (adjacent ranges are folded into one bigger range).

The timelines used by the objects returned by the buffered, seekable and played DOM attributes of media elements must be the same as that element's media resource's timeline.

3.12.10.12. Byte ranges

Objects implementing the ByteRanges interface represent a list of ranges of bytes.

interface ByteRanges {
  readonly attribute unsigned long length;
  unsigned long start(in unsigned long index);
  unsigned long end(in unsigned long index);
};

The length DOM attribute must return the number of ranges represented by the object.

The start(index) method must return the position of the first byte of the indexth range represented by the object.

The end(index) method must return the position of the byte immediately after the last byte of the indexth range represented by the object. (The byte position returned by this method is not in the range itself. If the first byte of the range is the byte at position 0, and the entire stream of bytes is in the range, then the value of the position of the byte returned by this method for that range will be the same as the number of bytes in the stream.)

These methods must raise INDEX_SIZE_ERR exceptions if called with an index argument greater than or equal to the number of ranges represented by the object.

When a ByteRanges object is said to be a normalized ByteRanges object, the ranges it represents must obey the following criteria:

In other words, the ranges in such an object are ordered, don't overlap, aren't empty, and don't touch (adjacent ranges are folded into one bigger range).

3.12.10.13. Event summary

The following events fire on media elements as part of the processing model described above:

Event name Interface Dispatched when... Preconditions
loadstart ProgressEvent [PROGRESS] The user agent begins fetching the media data, synchronously during the load() method call. networkState equals LOADING
progress ProgressEvent [PROGRESS] The user agent is fetching media data. networkState is more than EMPTY and less than LOADED
loadedmetadata Event The user agent is fetching media data, and the media resource's metadata has just been received. networkState equals LOADED_METADATA
loadedfirstframe Event The user agent is fetching media data, and the media resource's first frame has just been received. networkState equals LOADED_FIRST_FRAME
load ProgressEvent [PROGRESS] The user agent finishes downloading the entire media resource. networkState equals LOADED
abort ProgressEvent [PROGRESS] The user agent stops fetching the media data before it is completely downloaded. This can be fired synchronously during the load() method call. error is an object with the code MEDIA_ERR_ABORTED. networkState equals either EMPTY or LOADED, depending on when the download was aborted.
error ProgressEvent [PROGRESS] An error occurs while fetching the media data. error is an object with the code MEDIA_ERR_NETWORK_ERROR or higher. networkState equals either EMPTY or LOADED, depending on when the download was aborted.
emptied Event A media element whose networkState was previously not in the EMPTY state has just switched to that state (either because of a fatal error during load that's about to be reported, or because the load() method was reinvoked, in which case it is fired synchronously during the load() method call). networkState is EMPTY; all the DOM attributes are in their initial states.
stalled ProgressEvent The user agent is trying to fetch media data, but data is unexpectedly not forthcoming.
play Event Playback has begun. Fired after the play method has returned. paused is newly false.
pause Event Playback has been paused. Fired after the pause method has returned. paused is newly true.
waiting Event Playback has stopped because the next frame is not available, but the user agent expects that frame to become available in due course. readyState is either DATA_UNAVAILABLE or CAN_SHOW_CURRENT_FRAME, and paused is false. Either seeking is true, or the current playback position is not contained in any of the ranges in buffered. It is possible for playback to stop for two other reasons without paused being false, but those two reasons do not fire this event: maybe playback ended, or playback stopped due to errors.
seeking Event The seeking DOM attribute changed to true and the seek operation is taking long enough that the user agent has time to fire the event.
seeked Event The seeking DOM attribute changed to false.
timeupdate Event The current playback position changed in an interesting way, for example discontinuously.
ended Event Playback has stopped because the end of the media resource was reached. currentTime equals the effective end; ended is true.
dataunavailable Event The user agent cannot render the data at the current playback position because data for the current frame is not immediately available. The readyState attribute is newly equal to DATA_UNAVAILABLE.
canshowcurrentframe Event The user agent cannot render the data after the current playback position because data for the next frame is not immediately available. The readyState attribute is newly equal to CAN_SHOW_CURRENT_FRAME.
canplay Event The user agent can resume playback of the media data, but estimates that if playback were to be started now, the media resource could not be rendered at the current playback rate up to its end without having to stop for further buffering of content. The readyState attribute is newly equal to CAN_PLAY.
canplaythrough Event The user agent estimates that if playback were to be started now, the media resource could be rendered at the current playback rate all the way to its end without having to stop for further buffering. The readyState attribute is newly equal to CAN_PLAY_THROUGH.
ratechange Event Either the defaultPlaybackRate or the playbackRate attribute has just been updated.
durationchange Event The duration attribute has just been updated.
volumechange Event Either the volume attribute or the muted attribute has changed. Fired after the relevant attribute's setter has returned.
3.12.10.14. Security and privacy considerations

Talk about making sure interactive media files (e.g. SVG) don't have access to the container DOM (XSS potential); talk about not exposing any sensitive data like metadata from tracks in the media files (intranet snooping risk)

3.12.11 The canvas element

Categories
Embedded content.
Contexts in which this element may be used:
Where embedded content is expected.
Content model:
Transparent.
Element-specific attributes:
width
height
DOM interface:
interface HTMLCanvasElement : HTMLElement {
           attribute unsigned long width;
           attribute unsigned long height;

  DOMString toDataURL();
  DOMString toDataURL(in DOMString type);

  DOMObject getContext(in DOMString contextId);
};

The canvas element represents a resolution-dependent bitmap canvas, which can be used for rendering graphs, game graphics, or other visual images on the fly.

Authors should not use the canvas element in a document when a more suitable element is available. For example, it is inappropriate to use a canvas element to render a page heading: if the desired presentation of the heading is graphically intense, it should be marked up using appropriate elements (typically h1) and then styled using CSS and supporting technologies such as XBL.

When authors use the canvas element, they should also provide content that, when presented to the user, conveys essentially the same function or purpose as the bitmap canvas. This content may be placed as content of the canvas element. The contents of the canvas element, if any, are the element's fallback content.

In interactive visual media, if the canvas element is with script, the canvas element represents an embedded element with a dynamically created image.

In non-interactive, static, visual media, if the canvas element has been previously painted on (e.g. if the page was viewed in an interactive visual medium and is now being printed, or if some script that ran during the page layout process painted on the element), then the canvas element represents embedded content with the current image and size. Otherwise, the element represents its fallback content instead.

In non-visual media, and in visual media if the canvas element is without script, the canvas element represents its fallback content instead.

The canvas element has two attributes to control the size of the coordinate space: width and height. These attributes, when specified, must have values that are valid non-negative integers. The rules for parsing non-negative integers must be used to obtain their numeric values. If an attribute is missing, or if parsing its value returns an error, then the default value must be used instead. The width attribute defaults to 300, and the height attribute defaults to 150.

The intrinsic dimensions of the canvas element equal the size of the coordinate space, with the numbers interpreted in CSS pixels. However, the element can be sized arbitrarily by a style sheet. During rendering, the image is scaled to fit this layout size.

The size of the coordinate space does not necessarily represent the size of the actual bitmap that the user agent will use internally or during rendering. On high-definition displays, for instance, the user agent may internally use a bitmap with two device pixels per unit in the coordinate space, so that the rendering remains at high quality throughout.

Whenever the width and height attributes are set (whether to a new value or to the previous value), the bitmap and any associated contexts must be cleared back to their initial state and reinitialized with the newly specified coordinate space dimensions.

The width and height DOM attributes must reflect the content attributes of the same name.

Only one square appears to be drawn in the following example:

  // canvas is a reference to a <canvas> element
  var context = canvas.getContext('2d');
  context.fillRect(0,0,50,50);
  canvas.setAttribute('width', '300'); // clears the canvas
  context.fillRect(0,100,50,50);
  canvas.width = canvas.width; // clears the canvas
  context.fillRect(100,0,50,50); // only this square remains

When the canvas is initialized it must be set to fully transparent black.

To draw on the canvas, authors must first obtain a reference to a context using the getContext(contextId) method of the canvas element.

This specification only defines one context, with the name "2d". If getContext() is called with that exact string for its contextId argument, then the UA must return a reference to an object implementing CanvasRenderingContext2D. Other specifications may define their own contexts, which would return different objects.

Vendors may also define experimental contexts using the syntax vendorname-context, for example, moz-3d.

When the UA is passed an empty string or a string specifying a context that it does not support, then it must return null. String comparisons must be literal and case-sensitive.

Arguments other than the contextId must be ignored, and must not cause the user agent to raise an exception (as would normally occur if a method was called with the wrong number of arguments).

A future version of this specification will probably define a 3d context (probably based on the OpenGL ES API).

The toDataURL() method must, when called with no arguments, return a data: URI containing a representation of the image as a PNG file. [PNG].

If the canvas has no pixels (i.e. either its horizontal dimension or its vertical dimension is zero) then the method must return the string "data:,". (This is the shortest data: URI; it represents the empty string in a text/plain resource.)

The toDataURL(type) method (when called with one or more arguments) must return a data: URI containing a representation of the image in the format given by type. The possible values are MIME types with no parameters, for example image/png, image/jpeg, or even maybe image/svg+xml if the implementation actually keeps enough information to reliably render an SVG image from the canvas.

Only support for image/png is required. User agents may support other types. If the user agent does not support the requested type, it must return the image using the PNG format.

User agents must convert the provided type to lower case before establishing if they support that type and before creating the data: URI.

When trying to use types other than image/png, authors can check if the image was really returned in the requested format by checking to see if the returned string starts with one the exact strings "data:image/png," or "data:image/png;". If it does, the image is PNG, and thus the requested type was not supported. (The one exception to this is if the canvas has either no height or no width, in which case the result might simply be "data:,".)

Arguments other than the type must be ignored, and must not cause the user agent to raise an exception (as would normally occur if a method was called with the wrong number of arguments). A future version of this specification will probably allow extra parameters to be passed to toDataURL() to allow authors to more carefully control compression settings, image metadata, etc.

3.12.11.1. The 2D context

When the getContext() method of a canvas element is invoked with 2d as the argument, a CanvasRenderingContext2D object is returned.

There is only one CanvasRenderingContext2D object per canvas, so calling the getContext() method with the 2d argument a second time must return the same object.

The 2D context represents a flat Cartesian surface whose origin (0,0) is at the top left corner, with the coordinate space having x values increasing when going right, and y values increasing when going down.

interface CanvasRenderingContext2D {

  // back-reference to the canvas
  readonly attribute HTMLCanvasElement canvas;

  // state
  void save(); // push state on state stack
  void restore(); // pop state stack and restore state

  // transformations (default transform is the identity matrix)
  void scale(in float x, in float y);
  void rotate(in float angle);
  void translate(in float x, in float y);
  void transform(in float m11, in float m12, in float m21, in float m22, in float dx, in float dy);
  void setTransform(in float m11, in float m12, in float m21, in float m22, in float dx, in float dy);

  // compositing
           attribute float globalAlpha; // (default 1.0)
           attribute DOMString globalCompositeOperation; // (default source-over)

  // colors and styles
           attribute DOMObject strokeStyle; // (default black)
           attribute DOMObject fillStyle; // (default black)
  CanvasGradient createLinearGradient(in float x0, in float y0, in float x1, in float y1);
  CanvasGradient createRadialGradient(in float x0, in float y0, in float r0, in float x1, in float y1, in float r1);
  CanvasPattern createPattern(in HTMLImageElement image, in DOMString repetition);
  CanvasPattern createPattern(in HTMLCanvasElement image, in DOMString repetition);

  // line caps/joins
           attribute float lineWidth; // (default 1)
           attribute DOMString lineCap; // "butt", "round", "square" (default "butt")
           attribute DOMString lineJoin; // "round", "bevel", "miter" (default "miter")
           attribute float miterLimit; // (default 10)

  // shadows
           attribute float shadowOffsetX; // (default 0)
           attribute float shadowOffsetY; // (default 0)
           attribute float shadowBlur; // (default 0)
           attribute DOMString shadowColor; // (default transparent black)

  // rects
  void clearRect(in float x, in float y, in float w, in float h);
  void fillRect(in float x, in float y, in float w, in float h);
  void strokeRect(in float x, in float y, in float w, in float h);

  // path API
  void beginPath();
  void closePath();
  void moveTo(in float x, in float y);
  void lineTo(in float x, in float y);
  void quadraticCurveTo(in float cpx, in float cpy, in float x, in float y);
  void bezierCurveTo(in float cp1x, in float cp1y, in float cp2x, in float cp2y, in float x, in float y);
  void arcTo(in float x1, in float y1, in float x2, in float y2, in float radius);
  void rect(in float x, in float y, in float w, in float h);
  void arc(in float x, in float y, in float radius, in float startAngle, in float endAngle, in boolean anticlockwise);
  void fill();
  void stroke();
  void clip();
  boolean isPointInPath(in float x, in float y);

  // text
           attribute DOMString font; // (default 10px sans-serif)
           attribute DOMString textAlign; // "start", "end", "left", "right", "center" (default: "start")
           attribute DOMString textBaseline; // "top", "hanging", "middle", "alphabetic", "ideographic", "bottom" (default: "alphabetic")
  void fillText(in DOMString text, in float x, in float y);
  void fillText(in DOMString text, in float x, in float y, in float maxWidth);
  void strokeText(in DOMString text, in float x, in float y);
  void strokeText(in DOMString text, in float x, in float y, in float maxWidth);
  TextMetrics measureText(in DOMString text);

  // drawing images
  void drawImage(in HTMLImageElement image, in float dx, in float dy);
  void drawImage(in HTMLImageElement image, in float dx, in float dy, in float dw, in float dh);
  void drawImage(in HTMLImageElement image, in float sx, in float sy, in float sw, in float sh, in float dx, in float dy, in float dw, in float dh);
  void drawImage(in HTMLCanvasElement image, in float dx, in float dy);
  void drawImage(in HTMLCanvasElement image, in float dx, in float dy, in float dw, in float dh);
  void drawImage(in HTMLCanvasElement image, in float sx, in float sy, in float sw, in float sh, in float dx, in float dy, in float dw, in float dh);

  // pixel manipulation
  ImageData createImageData(in float sw, in float sh);
  ImageData getImageData(in float sx, in float sy, in float sw, in float sh);
  void putImageData(in ImageData imagedata, in float dx, in float dy);
  void putImageData(in ImageData imagedata, in float dx, in float dy, in float dirtyX, in float dirtyY, in float dirtyWidth, in float dirtyHeight);
};

interface CanvasGradient {
  // opaque object
  void addColorStop(in float offset, in DOMString color);
};

interface CanvasPattern {
  // opaque object
};

interface TextMetrics {
  readonly attribute float width;
};

interface ImageData {
  readonly attribute long int width;
  readonly attribute long int height;
  readonly attribute int[] data;
};

The canvas attribute must return the canvas element that the context paints on.

Unless otherwise stated, for the 2D context interface, any method call with a numeric argument whose value is infinite or a NaN value must be ignored.

3.12.11.1.1. The canvas state

Each context maintains a stack of drawing states. Drawing states consist of:

The current path and the current bitmap are not part of the drawing state. The current path is persistent, and can only be reset using the beginPath() method. The current bitmap is a property of the canvas, not the context.

The save() method must push a copy of the current drawing state onto the drawing state stack.

The restore() method must pop the top entry in the drawing state stack, and reset the drawing state it describes. If there is no saved state, the method must do nothing.

3.12.11.1.2. Transformations

The transformation matrix is applied to coordinates when creating shapes and paths.

When the context is created, the transformation matrix must initially be the identity transform. It may then be adjusted using the transformation methods.

The transformations must be performed in reverse order. For instance, if a scale transformation that doubles the width is applied, followed by a rotation transformation that rotates drawing operations by a quarter turn, and a rectangle twice as wide as it is tall is then drawn on the canvas, the actual result will be a square.

The scale(x, y) method must add the scaling transformation described by the arguments to the transformation matrix. The x argument represents the scale factor in the horizontal direction and the y argument represents the scale factor in the vertical direction. The factors are multiples.

The rotate(angle) method must add the rotation transformation described by the argument to the transformation matrix. The angle argument represents a clockwise rotation angle expressed in radians. If the angle argument is infinite, the method call must be ignored.

The translate(x, y) method must add the translation transformation described by the arguments to the transformation matrix. The x argument represents the translation distance in the horizontal direction and the y argument represents the translation distance in the vertical direction. The arguments are in coordinate space units.

The transform(m11, m12, m21, m22, dx, dy) method must multiply the current transformation matrix with the matrix described by:

m11 m21 dx
m12 m22 dy
0 0 1

The setTransform(m11, m12, m21, m22, dx, dy) method must reset the current transform to the identity matrix, and then invoke the transform(m11, m12, m21, m22, dx, dy) method with the same arguments.

3.12.11.1.3. Compositing

All drawing operations are affected by the global compositing attributes, globalAlpha and globalCompositeOperation.

The globalAlpha attribute gives an alpha value that is applied to shapes and images before they are composited onto the canvas. The value must be in the range from 0.0 (fully transparent) to 1.0 (no additional transparency). If an attempt is made to set the attribute to a value outside this range, the attribute must retain its previous value. When the context is created, the globalAlpha attribute must initially have the value 1.0.

The globalCompositeOperation attribute sets how shapes and images are drawn onto the existing bitmap, once they have had globalAlpha and the current transformation matrix applied. It must be set to a value from the following list. In the descriptions below, the source image, A, is the shape or image being rendered, and the destination image, B, is the current state of the bitmap.

source-atop
A atop B. Display the source image wherever both images are opaque. Display the destination image wherever the destination image is opaque but the source image is transparent. Display transparency elsewhere.
source-in
A in B. Display the source image wherever both the source image and destination image are opaque. Display transparency elsewhere.
source-out
A out B. Display the source image wherever the source image is opaque and the destination image is transparent. Display transparency elsewhere.
source-over (default)
A over B. Display the source image wherever the source image is opaque. Display the destination image elsewhere.
destination-atop
B atop A. Same as source-atop but using the destination image instead of the source image and vice versa.
destination-in
B in A. Same as source-in but using the destination image instead of the source image and vice versa.
destination-out
B out A. Same as source-out but using the destination image instead of the source image and vice versa.
destination-over
B over A. Same as source-over but using the destination image instead of the source image and vice versa.
lighter
A plus B. Display the sum of the source image and destination image, with color values approaching 1 as a limit.
copy
A (B is ignored). Display the source image instead of the destination image.
xor
A xor B. Exclusive OR of the source image and destination image.
vendorName-operationName
Vendor-specific extensions to the list of composition operators should use this syntax.

These values are all case-sensitive — they must be used exactly as shown. User agents must not recognize values that do not exactly match the values given above.

The operators in the above list must be treated as described by the Porter-Duff operator given at the start of their description (e.g. A over B). [PORTERDUFF]

On setting, if the user agent does not recognize the specified value, it must be ignored, leaving the value of globalCompositeOperation unaffected.

When the context is created, the globalCompositeOperation attribute must initially have the value source-over.

3.12.11.1.4. Colors and styles

The strokeStyle attribute represents the color or style to use for the lines around shapes, and the fillStyle attribute represents the color or style to use inside the shapes.

Both attributes can be either strings, CanvasGradients, or CanvasPatterns. On setting, strings must be parsed as CSS <color> values and the color assigned, and CanvasGradient and CanvasPattern objects must be assigned themselves. [CSS3COLOR] If the value is a string but is not a valid color, or is neither a string, a CanvasGradient, nor a CanvasPattern, then it must be ignored, and the attribute must retain its previous value.

On getting, if the value is a color, then the serialization of the color must be returned. Otherwise, if it is not a color but a CanvasGradient or CanvasPattern, then the respective object must be returned. (Such objects are opaque and therefore only useful for assigning to other attributes or for comparison to other gradients or patterns.)

The serialization of a color for a color value is a string, computed as follows: if it has alpha equal to 1.0, then the string is a lowercase six-digit hex value, prefixed with a "#" character (U+0023 NUMBER SIGN), with the first two digits representing the red component, the next two digits representing the green component, and the last two digits representing the blue component, the digits being in the range 0-9 a-f (U+0030 to U+0039 and U+0061 to U+0066). Otherwise, the color value has alpha less than 1.0, and the string is the color value in the CSS rgba() functional-notation format: the literal string rgba (U+0072 U+0067 U+0062 U+0061) followed by a U+0028 LEFT PARENTHESIS, a base-ten integer in the range 0-255 representing the red component (using digits 0-9, U+0030 to U+0039, in the shortest form possible), a literal U+002C COMMA and U+0020 SPACE, an integer for the green component, a comma and a space, an integer for the blue component, another comma and space, a U+0030 DIGIT ZERO, a U+002E FULL STOP (representing the decimal point), one or more digits in the range 0-9 (U+0030 to U+0039) representing the fractional part of the alpha value, and finally a U+0029 RIGHT PARENTHESIS.

When the context is created, the strokeStyle and fillStyle attributes must initially have the string value #000000.

There are two types of gradients, linear gradients and radial gradients, both represented by objects implementing the opaque CanvasGradient interface.

Once a gradient has been created (see below), stops are placed along it to define how the colors are distributed along the gradient. The color of the gradient at each stop is the color specified for that stop. Between each such stop, the colors and the alpha component must be linearly interpolated over the RGBA space without premultiplying the alpha value to find the color to use at that offset. Before the first stop, the color must be the color of the first stop. After the last stop, the color must be the color of the last stop. When there are no stops, the gradient is transparent black.

The addColorStop(offset, color) method on the CanvasGradient interface adds a new stop to a gradient. If the offset is less than 0, greater than 1, infinite, or NaN, then an INDEX_SIZE_ERR exception must be raised. If the color cannot be parsed as a CSS color, then a SYNTAX_ERR exception must be raised. Otherwise, the gradient must have a new stop placed, at offset offset relative to the whole gradient, and with the color obtained by parsing color as a CSS <color> value. If multiple stops are added at the same offset on a gradient, they must be placed in the order added, with the first one closest to the start of the gradient, and each subsequent one infinitesimally further along towards the end point (in effect causing all but the first and last stop added at each point to be ignored).

The createLinearGradient(x0, y0, x1, y1) method takes four arguments that, after being subjected to the current transformation matrix, represent the start point (x0, y0) and end point (x1, y1) of the gradient. If any of the arguments to createLinearGradient() are infinite or NaN, the method must raise an INDEX_SIZE_ERR exception. Otherwise, the method must return a linear CanvasGradient initialized with the specified line.

Linear gradients must be rendered such that at and before the starting point on the canvas the color at offset 0 is used, that at and after the ending point the color at offset 1 is used, and that all points on a line perpendicular to the line that crosses the start and end points have the color at the point where those two lines cross (with the colors coming from the interpolation described above).

If x0 = x1 and y0 = y1, then the linear gradient must paint nothing.

The createRadialGradient(x0, y0, r0, x1, y1, r1) method takes six arguments, the first three representing the start circle with origin (x0, y0) and radius r0, and the last three representing the end circle with origin (x1, y1) and radius r1. The values are in coordinate space units. If either of r0 or r1 are negative, or if any of the arguments are infinite or NaN, an INDEX_SIZE_ERR exception must be raised. Otherwise, the method must return a radial CanvasGradient initialized with the two specified circles, after transforming them according to the current transformation matrix.

Radial gradients must be rendered by following these steps:

  1. If x0 = x1 and y0 = y1 and r0 = r1, then the radial gradient must paint nothing. Abort these steps.

  2. Let x(ω) = (x1-x0)ω + x0

    Let y(ω) = (y1-y0)ω + y0

    Let r(ω) = (r1-r0)ω + r0

    Let the color at ω be the color of the gradient at offset 0.0 for all values of ω less than 0.0, the color at offset 1.0 for all values of ω greater than 1.0, and the color at the given offset for values of ω in the range 0.0 ≤ ω ≤ 1.0

  3. For all values of ω where r(ω) > 0, starting with the value of ω nearest to positive infinity and ending with the value of ω nearest to negative infinity, draw the circumference of the circle with radius r(ω) at position (x(ω), y(ω)), with the color at ω, but only painting on the parts of the canvas that have not yet been painted on by earlier circles in this step for this rendering of the gradient.

This effectively creates a cone, touched by the two circles defined in the creation of the gradient, with the part of the cone before the start circle (0.0) using the color of the first offset, the part of the cone after the end circle (1.0) using the color of the last offset, and areas outside the cone untouched by the gradient (transparent black).

Gradients must be painted only where the relevant stroking or filling effects requires that they be drawn.

Patterns are represented by objects implementing the opaque CanvasPattern interface.

To create objects of this type, the createPattern(image, repetition) method is used. The first argument gives the image to use as the pattern (either an HTMLImageElement or an HTMLCanvasElement). Modifying this image after calling the createPattern() method must not affect the pattern. The second argument must be a string with one of the following values: repeat, repeat-x, repeat-y, no-repeat. If the empty string or null is specified, repeat must be assumed. If an unrecognized value is given, then the user agent must raise a SYNTAX_ERR exception. User agents must recognize the four values described above exactly (e.g. they must not do case folding). The method must return a CanvasPattern object suitably initialized.

The image argument must be an instance of an HTMLImageElement or HTMLCanvasElement. If the image is of the wrong type or null, the implementation must raise a TYPE_MISMATCH_ERR exception.

If the image argument is an HTMLImageElement object whose complete attribute is false, then the implementation must raise an INVALID_STATE_ERR exception.

If the image argument is an HTMLCanvasElement object with either a horizontal dimension or a vertical dimension equal to zero, then the implementation must raise an INVALID_STATE_ERR exception.

Patterns must be painted so that the top left of the first image is anchored at the origin of the coordinate space, and images are then repeated horizontally to the left and right (if the repeat-x string was specified) or vertically up and down (if the repeat-y string was specified) or in all four directions all over the canvas (if the repeat string was specified). The images are not scaled by this process; one CSS pixel of the image must be painted on one coordinate space unit. Of course, patterns must actually be painted only where the stroking or filling effect requires that they be drawn, and are affected by the current transformation matrix.

When the createPattern() method is passed, as its image argument, an animated image, the poster frame of the animation, or the first frame of the animation if there is no poster frame, must be used.

Support for patterns is optional. If the user agent doesn't support patterns, then createPattern() must return null.

3.12.11.1.5. Line styles

The lineWidth attribute gives the width of lines, in coordinate space units. On setting, zero, negative, infinite, and NaN values must be ignored, leaving the value unchanged.

When the context is created, the lineWidth attribute must initially have the value 1.0.

The lineCap attribute defines the type of endings that UAs will place on the end of lines. The three valid values are butt, round, and square. The butt value means that the end of each line is a flat edge perpendicular to the direction of the line. The round value means that a semi-circle with the diameter equal to the width of the line must then be added on to the end of the line. The square value means that a rectangle with the length of the line width and the width of half the line width, placed flat against the edge perpendicular to the direction of the line, must be added at the end of each line. On setting, any other value than the literal strings butt, round, and square must be ignored, leaving the value unchanged.

When the context is created, the lineCap attribute must initially have the value butt.

The lineJoin attribute defines the type of corners that UAs will place where two lines meet. The three valid values are bevel, round, and miter.

On setting, any other value than the literal strings bevel, round, and miter must be ignored, leaving the value unchanged.

When the context is created, the lineJoin attribute must initially have the value miter.

A join exists at any point in a subpath shared by two consecutive lines. When a subpath is closed, then a join also exists at its first point (equivalent to its last point) connecting the first and last lines in the subpath.

In addition to the point where the join occurs, two additional points are relevant to each join, one for each line: the two corners found half the line width away from the join point, one perpendicular to each line, each on the side furthest from the other line.

A filled triangle connecting these two opposite corners with a straight line, with the third point of the triangle being the join point, must be rendered at all joins. The lineJoin attribute controls whether anything else is rendered. The three aforementioned values have the following meanings:

The bevel value means that this is all that is rendered at joins.

The round value means that a filled arc connecting the two aforementioned corners of the join, abutting (and not overlapping) the aforementioned triangle, with the diameter equal to the line width and the origin at the point of the join, must be rendered at joins.

The miter value means that a second filled triangle must (if it can given the miter length) be rendered at the join, with one line being the line between the two aforementioned corners, abutting the first triangle, and the other two being continuations of the outside edges of the two joining lines, as long as required to intersect without going over the miter length.

The miter length is the distance from the point where the lines touch on the inside of the join to the intersection of the line edges on the outside of the join. The miter limit ratio is the maximum allowed ratio of the length of the two continuation lines to the line width. If the miter length would be exceeded, this second triangle must not be rendered.

The miter limit ratio can be explicitly set using the miterLimit attribute. On setting, zero, negative, infinite, and NaN values must be ignored, leaving the value unchanged.

When the context is created, the miterLimit attribute must initially have the value 10.0.

3.12.11.1.6. Shadows

All drawing operations are affected by the four global shadow attributes.

The shadowColor attribute sets the color of the shadow.

When the context is created, the shadowColor attribute initially must be fully-transparent black.

On getting, the serialization of the color must be returned.

On setting, the new value must be parsed as a CSS <color> value and the color assigned. If the value is not a valid color, then it must be ignored, and the attribute must retain its previous value. [CSS3COLOR]

The shadowOffsetX and shadowOffsetY attributes specify the distance that the shadow will be offset in the positive horizontal and positive vertical distance respectively. Their values are in coordinate space units. They are not affected by the current transformation matrix.

When the context is created, the shadow offset attributes initially have the value 0.

On getting, they must return their current value. On setting, the attribute being set must be set to the new value, except if the value is infinite or NaN, in which case the new value must be ignored.

The shadowBlur attribute specifies the size of the blurring effect. (The units do not map to coordinate space units, and are not affected by the current transformation matrix.)

When the context is created, the shadowBlur attribute must initially have the value 0.

On getting, the attribute must return its current value. On setting the attribute must be set to the new value, except if the value is negative, infinite or NaN, in which case the new value must be ignored.

Support for shadows is optional. When they are supported, then, when shadows are drawn, they must be rendered as follows:

  1. Let A be the source image for which a shadow is being created.

  2. Let B be an infinite transparent black bitmap, with a coordinate space and an origin identical to A.

  3. Copy the alpha channel of A to B, offset by shadowOffsetX in the positive x direction, and shadowOffsetY in the positive y direction.

  4. If shadowBlur is greater than 0:

    1. If shadowBlur is less than 8, let σ be half the value of shadowBlur; otherwise, let σ be the square root of multiplying the value of shadowBlur by 2.

    2. Perform a 2D Gaussian Blur on B, using σ as the standard deviation.

    User agents may limit values of σ to an implementation-specific maximum value to avoid exceeding hardware limitations during the Gaussian blur operation.

  5. Set the red, green, and blue components of every pixel in B to the red, green, and blue components (respectively) of the color of shadowColor.

  6. Multiply the alpha component of every pixel in B by the alpha component of the color of shadowColor.

  7. The shadow is in the bitmap B, and is rendered as part of the drawing model described below.

3.12.11.1.7. Simple shapes (rectangles)

There are three methods that immediately draw rectangles to the bitmap. They each take four arguments; the first two give the x and y coordinates of the top left of the rectangle, and the second two give the width w and height h of the rectangle, respectively.

The current transformation matrix must be applied to the following four coordinates, which form the path that must then be closed to get the specified rectangle: (x, y), (x+w, y), (x+w, y+h), (x, y+h).

Shapes are painted without affecting the current path, and are subject to the clipping region, and, with the exception of clearRect(), also shadow effects, global alpha, and global composition operators.

The clearRect(x, y, w, h) method must clear the pixels in the specified rectangle that also intersect the current clipping region to a fully transparent black, erasing any previous image. If either height or width are zero, this method has no effect.

The fillRect(x, y, w, h) method must paint the specified rectangular area using the fillStyle. If either height or width are zero, this method has no effect.

The strokeRect(x, y, w, h) method must stroke the specified rectangle's path using the strokeStyle, lineWidth, lineJoin, and (if appropriate) miterLimit attributes. If both height and width are zero, this method has no effect, since there is no path to stroke (it's a point). If only one of the two is zero, then the method will draw a line instead (the path for the outline is just a straight line along the non-zero dimension).

3.12.11.1.8. Complex shapes (paths)

The context always has a current path. There is only one current path, it is not part of the drawing state.

A path has a list of zero or more subpaths. Each subpath consists of a list of one or more points, connected by straight or curved lines, and a flag indicating whether the subpath is closed or not. A closed subpath is one where the last point of the subpath is connected to the first point of the subpath by a straight line. Subpaths with fewer than two points are ignored when painting the path.

Initially, the context's path must have zero subpaths.

The points and lines added to the path by these methods must be transformed according to the current transformation matrix as they are added.

The beginPath() method must empty the list of subpaths so that the context once again has zero subpaths.

The moveTo(x, y) method must create a new subpath with the specified point as its first (and only) point.

The closePath() method must do nothing if the context has no subpaths. Otherwise, it must mark the last subpath as closed, create a new subpath whose first point is the same as the previous subpath's first point, and finally add this new subpath to the path. (If the last subpath had more than one point in its list of points, then this is equivalent to adding a straight line connecting the last point back to the first point, thus "closing" the shape, and then repeating the last moveTo() call.)

New points and the lines connecting them are added to subpaths using the methods described below. In all cases, the methods only modify the last subpath in the context's paths.

The lineTo(x, y) method must do nothing if the context has no subpaths. Otherwise, it must connect the last point in the subpath to the given point (x, y) using a straight line, and must then add the given point (x, y) to the subpath.

The quadraticCurveTo(cpx, cpy, x, y) method must do nothing if the context has no subpaths. Otherwise it must connect the last point in the subpath to the given point (x, y) using a quadratic Bézier curve with control point (cpx, cpy), and must then add the given point (x, y) to the subpath. [BEZIER]

The bezierCurveTo(cp1x, cp1y, cp2x, cp2y, x, y) method must do nothing if the context has no subpaths. Otherwise, it must connect the last point in the subpath to the given point (x, y) using a cubic Bézier curve with control points (cp1x, cp1y) and (cp2x, cp2y). Then, it must add the point (x, y) to the subpath. [BEZIER]

The arcTo(x1, y1, x2, y2, radius) method must do nothing if the context has no subpaths. If the context does have a subpath, then the behavior depends on the arguments and the last point in the subpath.

Negative values for radius must cause the implementation to raise an INDEX_SIZE_ERR exception.

Let the point (x0, y0) be the last point in the subpath.

If the point (x0, y0) is equal to the point (x1, y1), or if the point (x1, y1) is equal to the point (x2, y2), then the method must add the point (x1, y1) to the subpath, and connect that point to the previous point (x0, y0) by a straight line.

Otherwise, if the points (x0, y0), (x1, y1), and (x2, y2) all lie on a single straight line, then: if the direction from (x0, y0) to (x1, y1) is the same as the direction from (x1, y1) to (x2, y2), then method must add the point (x1, y1) to the subpath, and connect that point to the previous point (x0, y0) by a straight line; otherwise, the direction from (x0, y0) to (x1, y1) is the opposite of the direction from (x1, y1) to (x2, y2), and the method must add a point (x, y) to the subpath, and connect that point to the previous point (x0, y0) by a straight line, where (x, y) is the point that is infinitely far away from (x1, y1), that lies on the same line as (x0, y0), (x1, y1), and (x2, y2), and that is on the same side of (x1, y1) on that line as (x2, y2).

Otherwise, let The Arc be the shortest arc given by circumference of the circle that has radius radius, and that has one point tangent to the half-infinite line that crosses the point (x0, y0) and ends at the point (x1, y1), and that has a different point tangent to the half-infinite line that ends at the point (x1, y1) and crosses the point (x2, y2). The points at which this circle touches these two lines are called the start and end tangent points respectively.

The method must connect the point (x0, y0) to the start tangent point by a straight line, adding the start tangent point to the subpath, and then must connect the start tangent point to the end tangent point by The Arc, adding the end tangent point to the subpath.

The arc(x, y, radius, startAngle, endAngle, anticlockwise) method draws an arc. If the context has any subpaths, then the method must add a straight line from the last point in the subpath to the start point of the arc. In any case, it must draw the arc between the start point of the arc and the end point of the arc, and add the start and end points of the arc to the subpath. The arc and its start and end points are defined as follows:

Consider a circle that has its origin at (x, y) and that has radius radius. The points at startAngle and endAngle along the circle's circumference, measured in radians clockwise from the positive x-axis, are the start and end points respectively. The arc is the path along the circumference of this circle from the start point to the end point, going anti-clockwise if the anticlockwise argument is true, and clockwise otherwise. Since the points are on the circle, as opposed to being simply angles from zero, the arc can never cover an angle greater than 2π radians. If the two angles are equal, or if the radius is zero, then the arc is defined as being of zero length in both directions.

Negative values for radius must cause the implementation to raise an INDEX_SIZE_ERR exception.

The rect(x, y, w, h) method must create a new subpath containing just the four points (x, y), (x+w, y), (x+w, y+h), (x, y+h), with those four points connected by straight lines, and must then mark the subpath as closed. It must then create a new subpath with the point (x, y) as the only point in the subpath.

The fill() method must fill all the subpaths of the current path, using fillStyle, and using the non-zero winding number rule. Open subpaths must be implicitly closed when being filled (without affecting the actual subpaths).

Thus, if two overlapping but otherwise independent subpaths have opposite windings, they cancel out and result in no fill. If they have the same winding, that area just gets painted once.

The stroke() method must calculate the strokes of all the subpaths of the current path, using the lineWidth, lineCap, lineJoin, and (if appropriate) miterLimit attributes, and then fill the combined stroke area using the strokeStyle, attribute.

Since the subpaths are all stroked as one, overlapping parts of the paths in one stroke operation are treated as if their union was what was painted.

Paths, when filled or stroked, must be painted without affecting the current path, and must be subject to shadow effects, global alpha, the clipping region, and global composition operators. (Transformations affect the path when the path is created, not when it is painted, though the stroke style is still affected by the transformation during painting.)

Zero-length line segments must be pruned before stroking a path. Empty subpaths must be ignored.

The clip() method must create a new clipping region by calculating the intersection of the current clipping region and the area described by the current path, using the non-zero winding number rule. Open subpaths must be implicitly closed when computing the clipping region, without affecting the actual subpaths. The new clipping region replaces the current clipping region.

When the context is initialized, the clipping region must be set to the rectangle with the top left corner at (0,0) and the width and height of the coordinate space.

The isPointInPath(x, y) method must return true if the point given by the x and y coordinates passed to the method, when treated as coordinates in the canvas coordinate space unaffected by the current transformation, is inside the current path; and must return false otherwise. Points on the path itself are considered to be inside the path. If either of the arguments is infinite or NaN, then the method must return false.

3.12.11.1.9. Text

The font DOM attribute, on setting, must be parsed the same way as the 'font' property of CSS (but without supporting property-independent stylesheet syntax like 'inherit'), and the resulting font must be assigned to the context, with the 'line-height' component forced to 'normal'. [CSS]

Font names must be interpreted in the context of the canvas element's stylesheets; any fonts embedded using @font-face must therefore be available. [CSSWEBFONTS]

Only vector fonts should be used by the user agent; if a user agent were to use bitmap fonts then transformations would likely make the font look very ugly.

On getting, the font attribute must return the serialized form of the current font of the context. [CSSOM]

When the context is created, the font of the context must be set to 10px sans-serif. When the 'font-size' component is set to lengths using percentages, 'em' or 'ex' units, or the 'larger' or 'smaller' keywords, these must be interpreted relative to the computed value of the 'font-size' property of the corresponding canvas element. When the 'font-weight' component is set to the relative values 'bolder' and 'lighter', these must be interpreted relative to the computed value of the 'font-weight' property of the corresponding canvas element.

The textAlign DOM attribute, on getting, must return the current value. On setting, if the value is one of start, end, left, right, or center, then the value must be changed to the new value. Otherwise, the new value must be ignored. When the context is created, the textAlign attribute must initially have the value start.

The textBaseline DOM attribute, on getting, must return the current value. On setting, if the value is one of top, hanging, middle, alphabetic, ideographic, or bottom, then the value must be changed to the new value. Otherwise, the new value must be ignored. When the context is created, the textBaseline attribute must initially have the value alphabetic.

The textBaseline attribute's allowed keywords correspond to alignment points in the font:

The top of the em square is roughly at the top of the glyphs
   in a font, the hanging baseline is where some glyphs like आ are
   anchored, the middle is half-way between the top of the em square and the
   bottom of the em square, the alphabetic baseline is where characters like
   Á, ÿ, f, and Ω are anchored, the ideographic
   baseline is where glyphs like 私 and 達 are anchored, and the
   bottom of the em square is roughly at the bottom of the glyphs in a font.
   The top and bottom of the bounding box can be far from these baselines,
   due to glyphs extending far outside the em square.

The keywords map to these alignment points as follows:

top
The top of the em square
hanging
The hanging baseline
middle
The middle of the em square
alphabetic
The alphabetic baseline
ideographic
The ideographic baseline
bottom
The bottom of the em square

The fillText() and strokeText() methods take three or four arguments, text, x, y, and optionally maxWidth, and render the given text at the given (x, y) coordinates ensuring that the text isn't wider than maxWidth if specified, using the current font, textAlign, and textBaseline values. Specifically, when the methods are called, the user agent must run the following steps:

  1. Let font be the current font of the browsing context, as given by the font attribute.

  2. Replace all the space characters in text with U+0020 SPACE characters.

  3. Form a hypothetical infinitely wide CSS line box containing a single inline box containing the text text, with all the properties at their initial values except the 'font' property of the inline element set to font and the 'direction' property of the inline element set to the 'direction' property of the canvas element. [CSS]

  4. If the maxWidth argument was specified and the hypothetical width of the inline box in the hypothetical line box is greater than maxWidth CSS pixels, then change font to have a more condensed font (if one is available or if a reasonably readable one can be synthesized by applying a horizontal scale factor to the font) or a smaller font, and return to the previous step.

  5. Let the anchor point be a point on the inline box, determined by the textAlign and textBaseline values, as follows:

    Horizontal position:

    If textAlign is left
    If textAlign is start and the 'direction' property on the canvas element has a computed value of 'ltr'
    If textAlign is end and the 'direction' property on the canvas element has a computed value of 'rtl'
    Let the anchor point's horizontal position be the left edge of the inline box.
    If textAlign is right
    If textAlign is end and the 'direction' property on the canvas element has a computed value of 'ltr'
    If textAlign is start and the 'direction' property on the canvas element has a computed value of 'rtl'
    Let the anchor point's horizontal position be the right edge of the inline box.
    If textAlign is center
    Let the anchor point's horizontal position be half way between the left and right edges of the inline box.

    Vertical position:

    If textBaseline is top
    Let the anchor point's vertical position be the top of the em box of the first available font of the inline box.
    If textBaseline is hanging
    Let the anchor point's vertical position be the hanging baseline of the first available font of the inline box.
    If textBaseline is middle
    Let the anchor point's vertical position be half way between the bottom and the top of the em box of the first available font of the inline box.
    If textBaseline is alphabetic
    Let the anchor point's vertical position be the alphabetic baseline of the first available font of the inline box.
    If textBaseline is ideographic
    Let the anchor point's vertical position be the ideographic baseline of the first available font of the inline box.
    If textBaseline is bottom
    Let the anchor point's vertical position be the bottom of the em box of the first available font of the inline box.
  6. Paint the hypothetical inline box as the shape given by the text's glyphs, as transformed by the current transformation matrix, and anchored and sized so that before applying the current transformation matrix, the anchor point is at (x, y) and each CSS pixel is mapped to one coordinate space unit.

    For fillText() fillStyle must be applied to the glyphs and strokeStyle must be ignored. For strokeText() the reverse holds and strokeStyle must be applied to the glyph outlines and fillStyle must be ignored.

    Text is painted without affecting the current path, and is subject to shadow effects, global alpha, the clipping region, and global composition operators.

The measureText() method takes one argument, text. When the method is invoked, the user agent must replace all the space characters in text with U+0020 SPACE characters, and then must form a hypothetical infinitely wide CSS line box containing a single inline box containing the text text, with all the properties at their initial values except the 'font' property of the inline element set to the current font of the browsing context, as given by the font attribute, and must then return a new TextMetrics object with its width attribute set to the width of that inline box, in CSS pixels. [CSS]

The TextMetrics interface is used for the objects returned from measureText(). It has one attribute, width, which is set by the measureText() method.

Glyphs rendered using fillText() and strokeText() can spill out of the box given by the font size (the em square size) and the width returned by measureText() (the text width). This version of the specification does not provide a way to obtain the bounding box dimensions of the text. If the text is to be rendered and removed, care needs to be taken to replace the entire area of the canvas that the clipping region covers, not just the box given by the em square height and measured text width.

A future version of the 2D context API may provide a way to render fragments of documents, rendered using CSS, straight to the canvas. This would be provided in preference to a dedicated way of doing multiline layout.

3.12.11.1.10. Images

To draw images onto the canvas, the drawImage method can be used.

This method is overloaded with three variants: drawImage(image, dx, dy), drawImage(image, dx, dy, dw, dh), and drawImage(image, sx, sy, sw, sh, dx, dy, dw, dh). (Actually it is overloaded with six; each of those three can take either an HTMLImageElement or an HTMLCanvasElement for the image argument.) If not specified, the dw and dh arguments must default to the values of sw and sh, interpreted such that one CSS pixel in the image is treated as one unit in the canvas coordinate space. If the sx, sy, sw, and sh arguments are omitted, they must default to 0, 0, the image's intrinsic width in image pixels, and the image's intrinsic height in image pixels, respectively.

The image argument must be an instance of an HTMLImageElement or HTMLCanvasElement. If the image is of the wrong type or null, the implementation must raise a TYPE_MISMATCH_ERR exception.

If the image argument is an HTMLImageElement object whose complete attribute is false, then the implementation must raise an INVALID_STATE_ERR exception.

The source rectangle is the rectangle whose corners are the four points (sx, sy), (sx+sw, sy), (sx+sw, sy+sh), (sx, sy+sh).

If the source rectangle is not entirely within the source image, or if one of the sw or sh arguments is zero, the implementation must raise an INDEX_SIZE_ERR exception.

The destination rectangle is the rectangle whose corners are the four points (dx, dy), (dx+dw, dy), (dx+dw, dy+dh), (dx, dy+dh).

When drawImage() is invoked, the region of the image specified by the source rectangle must be painted on the region of the canvas specified by the destination rectangle, after applying the current transformation matrix to the points of the destination rectangle.

When a canvas is drawn onto itself, the drawing model requires the source to be copied before the image is drawn back onto the canvas, so it is possible to copy parts of a canvas onto overlapping parts of itself.

When the drawImage() method is passed, as its image argument, an animated image, the poster frame of the animation, or the first frame of the animation if there is no poster frame, must be used.

Images are painted without affecting the current path, and are subject to shadow effects, global alpha, the clipping region, and global composition operators.

3.12.11.1.11. Pixel manipulation

The createImageData(sw, sh) method must return an ImageData object representing a rectangle with a width in CSS pixels equal to the absolute magnitude of sw and a height in CSS pixels equal to the absolute magnitude of sh, filled with transparent black.

The getImageData(sx, sy, sw, sh) method must return an ImageData object representing the underlying pixel data for the area of the canvas denoted by the rectangle whose corners are the four points (sx, sy), (sx+sw, sy), (sx+sw, sy+sh), (sx, sy+sh), in canvas coordinate space units. Pixels outside the canvas must be returned as transparent black. Pixels must be returned as non-premultiplied alpha values.

If any of the arguments to createImageData() or getImageData() are infinite or NaN, or if either the sw or sh arguments are zero, the method must instead raise an INDEX_SIZE_ERR exception.

ImageData objects must be initialized so that their width attribute is set to w, the number of physical device pixels per row in the image data, their height attribute is set to h, the number of rows in the image data, and the data attribute is initialized to an array of h×w×4 integers. The pixels must be represented in this array in left-to-right order, row by row, starting at the top left, with each pixel's red, green, blue, and alpha components being given in that order. Each component of each device pixel represented in this array must be in the range 0..255, representing the 8 bit value for that component. At least one pixel must be returned.

The values of the data array may be changed (the length of the array, and the other attributes in ImageData objects, are all read-only). On setting, JS undefined values must be converted to zero. Other values must first be converted to numbers using JavaScript's ToNumber algorithm, and if the result is a NaN value, a TYPE_MISMATCH_ERR exception must be raised. If the result is less than 0, it must be clamped to zero. If the result is more than 255, it must be clamped to 255. If the number is not an integer, it must be rounded to the nearest integer using the IEEE 754r roundTiesToEven rounding mode. [ECMA262] [IEEE754R]

The width and height (w and h) might be different from the sw and sh arguments to the above methods, e.g. if the canvas is backed by a high-resolution bitmap, or if the sw and sh arguments are negative.

The putImageData(imagedata, dx, dy, dirtyX, dirtyY, dirtyWidth, dirtyHeight) method writes data from ImageData structures back to the canvas.

If the first argument to the method is null or not an ImageData object that was returned by createImageData() or getImageData() then the putImageData() method must raise a TYPE_MISMATCH_ERR exception.

If any of the arguments to the method are infinite or NaN, the method must raise an INDEX_SIZE_ERR exception.

When the last four arguments are omitted, they must be assumed to have the values 0, 0, the width member of the imagedata structure, and the heightmember of the imagedata structure, respectively.

When invoked with arguments that do not, per the last few paragraphs, cause an exception to be raised, the putImageData() method must act as follows:

  1. Let dxdevice be the x-coordinate of the device pixel in the underlying pixel data of the canvas corresponding to the dx coordinate in the canvas coordinate space.

    Let dydevice be the y-coordinate of the device pixel in the underlying pixel data of the canvas corresponding to the dy coordinate in the canvas coordinate space.

  2. If dirtyWidth is negative, let dirtyX be dirtyX+dirtyWidth, and let dirtyWidth be equal to the absolute magnitude of dirtyWidth.

    If dirtyHeight is negative, let dirtyY be dirtyY+dirtyHeight, and let dirtyHeight be equal to the absolute magnitude of dirtyHeight.

  3. If dirtyX is negative, let dirtyWidth be dirtyWidth+dirtyX, and let dirtyX be zero.

    If dirtyY is negative, let dirtyHeight be dirtyHeight+dirtyY, and let dirtyY be zero.

  4. If dirtyX+dirtyWidth is greater than the width attribute of the imagedata argument, let dirtyWidth be the value of that width attribute, minus the value of dirtyX.

    If dirtyY+dirtyHeight is greater than the height attribute of the imagedata argument, let dirtyHeight be the value of that height attribute, minus the value of dirtyY.

  5. If, after those changes, either dirtyWidth or dirtyHeight is negative or zero, stop these steps without affecting the canvas.

  6. Otherwise, for all values of x and y where dirtyX ≤ x < dirtyX+dirtyWidth and dirtyY ≤ y < dirtyY+dirtyHeight, copy the four channels of the pixel with coordinate (x, y) in the imagedata data structure to the pixel with coordinate (xdevice+x, ydevice+y) in the underlying pixel data of the canvas.

The handling of pixel rounding when the specified coordinates do not exactly map to the device coordinate space is not defined by this specification, except that the following must result in no visible changes to the rendering:

context.putImageData(context.getImageData(x, y, w, h), x, y);

...for any value of x and y. In other words, while user agents may round the arguments of the two methods so that they map to device pixel boundaries, any rounding performed must be performed consistently for both the getImageData() and putImageData() operations.

The current path, transformation matrix, shadow attributes, global alpha, the clipping region, and global composition operator must not affect the getImageData() and putImageData() methods.

The data returned by getImageData() is at the resolution of the canvas backing store, which is likely to not be one device pixel to each CSS pixel if the display used is a high resolution display. Thus, while one could create an ImageData object, one would not necessarily know what resolution the canvas expected (how many pixels the canvas wants to paint over one coordinate space unit pixel).

In the following example, the script first obtains the size of the canvas backing store, and then generates a few new ImageData objects which can be used.

  // canvas is a reference to a <canvas> element
  var context = canvas.getContext('2d');

  // create a blank slate
  var data = context.createImageData(canvas.width, canvas.height);

  // create some plasma
  FillPlasma(data, 'green'); // green plasma

  // add a cloud to the plasma
  AddCloud(data, data.width/2, data.height/2); // put a cloud in the middle

  // paint the plasma+cloud on the canvas
  context.putImageData(data, 0, 0);

  // support methods
  function FillPlasma(data, color) { ... }
  function AddCloud(data, x, y) { ... }

Here is an example of using getImageData() and putImageData() to implement an edge detection filter.

<!DOCTYPE HTML>
<html>
 <head>
  <title>Edge detection demo</title>
  <script>
   var image = new Image();
   function init() {
     image.onload = demo;
     image.src = "image.jpeg";
   }
   function demo() {
     var canvas = document.getElementsByTagName('canvas')[0];
     var context = canvas.getContext('2d');

     // draw the image onto the canvas
     context.drawImage(image, 0, 0);

     // get the image data to manipulate
     var input = context.getImageData(0, 0, canvas.width, canvas.height);

     // get an empty slate to put the data into
     var output = context.crateImageData(canvas.width, canvas.height);

     // alias some variables for convenience
     // notice that we are using input.width and input.height here
     // as they might not be the same as canvas.width and canvas.height
     // (in particular, they might be different on high-res displays)
     var w = input.width, h = input.height;
     var inputData = input.data;
     var outputData = output.data;

     // edge detection
     for (var y = 1; y < h-1; y += 1) {
       for (var x = 1; x < w-1; x += 1) {
         for (var c = 0; c < 3; c += 1) {
           var i = (y*w + x)*4 + c;
           outputData[i] = 127 + -inputData[i - w*4 - 4] -   inputData[i - w*4] - inputData[i - w*4 + 4] +
                                 -inputData[i - 4]       + 8*inputData[i]       - inputData[i + 4] +
                                 -inputData[i + w*4 - 4] -   inputData[i + w*4] - inputData[i + w*4 + 4];
         }
         outputData[(y*w + x)*4 + 3] = 255; // alpha
       }
     }

     // put the image data back after manipulation
     context.putImageData(output, 0, 0);
   }
  </script>
 </head>
 <body onload="init()">
  <canvas></canvas>
 </body>
</html>
3.12.11.1.12. Drawing model

When a shape or image is painted, user agents must follow these steps, in the order given (or act as if they do):

  1. Render the shape or image, creating image A, as described in the previous sections. For shapes, the current fill, stroke, and line styles must be honored, and the stroke must itself also be subjected to the current transformation matrix.

  2. If shadows are supported:

    1. Render the shadow from image A, using the current shadow styles, creating image B.

    2. Multiply the alpha component of every pixel in B by globalAlpha.

    3. Within the clipping region, composite B over the current canvas bitmap using the current composition operator.

  3. Multiply the alpha component of every pixel in A by globalAlpha.

  4. Within the clipping region, composite A over the current canvas bitmap using the current composition operator.

3.12.11.2. Color spaces and color correction

The canvas APIs must perform color correction at only two points: when rendering images with their own gamma correction and color space information onto the canvas, to convert the image to the color space used by the canvas (e.g. using the drawImage() method with an HTMLImageElement object), and when rendering the actual canvas bitmap to the output device.

Thus, in the 2D context, colors used to draw shapes onto the canvas will exactly match colors obtained through the getImageData() method.

The toDataURL() method must not include color space information in the resource returned. Where the output format allows it, the color of pixels in resources created by toDataURL() must match those returned by the getImageData() method.

In user agents that support CSS, the color space used by a canvas element must match the color space used for processing any colors for that element in CSS.

The gamma correction and color space information of images must be handled in such a way that an image rendered directly using an img element would use the same colors as one painted on a canvas element that is then itself rendered. Furthermore, the rendering of images that have no color correction information (such as those returned by the toDataURL() method) must be rendered with no color correction.

Thus, in the 2D context, calling the drawImage() method to render the output of the toDataURL() method to the canvas, given the appropriate dimensions, has no visible effect.

3.12.11.3. Security with canvas elements

Information leakage can occur if scripts from one origin are exposed to images from another origin (one that isn't the same).

To mitigate this, canvas elements are defined to have a flag indicating whether they are origin-clean. All canvas elements must start with their origin-clean set to true. The flag must be set to false if any of the following actions occur:

Whenever the toDataURL() method of a canvas element whose origin-clean flag is set to false is called, the method must immediately raise a security exception.

Whenever the getImageData() method of the 2D context of a canvas element whose origin-clean flag is set to false is called, the method must immediately raise a security exception.

3.12.12 The map element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
Flow content.
Element-specific attributes:
name
DOM interface:
interface HTMLMapElement : HTMLElement {
           attribute DOMString name;
  readonly attribute HTMLCollection areas;
  readonly attribute HTMLCollection images;
};

The map element, in conjunction with any area element descendants, defines an image map.

The name attribute gives the map a name so that it can be referenced. The attribute must be present and must have a non-empty value. Whitespace is significant in this attribute's value. If the id attribute is also specified, both attributes must have the same value.

The areas attribute must return an HTMLCollection rooted at the map element, whose filter matches only area elements.

The images attribute must return an HTMLCollection rooted at the Document node, whose filter matches only img and object elements that are associated with this map element according to the image map processing model.

The DOM attribute name must reflect the content attribute of the same name.

3.12.13 The area element

Categories
Phrasing content.
Contexts in which this element may be used:
Where phrasing content is expected, but only if there is a map element ancestor.
Content model:
Empty.
Element-specific attributes:
alt
coords
shape
href
target
ping
rel
media
hreflang
type
DOM interface:
interface HTMLAreaElement : HTMLElement {
           attribute DOMString alt;
           attribute DOMString coords;
           attribute DOMString shape;
           attribute DOMString href;
           attribute DOMString target;
           attribute DOMString ping;
           attribute DOMString rel;
  readonly attribute DOMTokenList relList;
           attribute DOMString media;
           attribute DOMString hreflang;
           attribute DOMString type;
};

The area element represents either a hyperlink with some text and a corresponding area on an image map, or a dead area on an image map.

If the area element has an href attribute, then the area element represents a hyperlink; the alt attribute, which must then be present, specifies the text.

However, if the area element has no href attribute, then the area represented by the element cannot be selected, and the alt attribute must be omitted.

In both cases, the shape and coords attributes specify the area.

The shape attribute is an enumerated attribute. The following table lists the keywords defined for this attribute. The states given in the first cell of the rows with keywords give the states to which those keywords map. Some of the keywords are non-conforming, as noted in the last column.

State Keywords Notes
Circle state circ Non-conforming
circle
Default state default
Polygon state poly
polygon Non-conforming
Rectangle state rect
rectangle Non-conforming

The attribute may be omitted. The missing value default is the rectangle state.

The coords attribute must, if specified, contain a valid list of integers. This attribute gives the coordinates for the shape described by the shape attribute. The processing for this attribute is described as part of the image map processing model.

In the circle state, area elements must have a coords attribute present, with three integers, the last of which must be non-negative. The first integer must be the distance in CSS pixels from the left edge of the image to the center of the circle, the second integer must be the distance in CSS pixels from the top edge of the image to the center of the circle, and the third integer must be the radius of the circle, again in CSS pixels.

In the default state state, area elements must not have a coords attribute.

In the polygon state, area elements must have a coords attribute with at least six integers, and the number of integers must be even. Each pair of integers must represent a coordinate given as the distances from the left and the top of the image in CSS pixels respectively, and all the coordinates together must represent the points of the polygon, in order.

In the rectangle state, area elements must have a coords attribute with exactly four integers, the first of which must be less than the third, and the second of which must be less than the fourth. The four points must represent, respectively, the distance from the left edge of the image to the top left side of the rectangle, the distance from the top edge to the top side, the distance from the left edge to the right side, and the distance from the top edge to the bottom side, all in CSS pixels.

When user agents allow users to follow hyperlinks created using the area element, as described in the next section, the href, target and ping attributes decide how the link is followed. The rel, media, hreflang, and type attributes may be used to indicate to the user the likely nature of the target resource before the user follows the link.

The target, ping, rel, media, hreflang, and type attributes must be omitted if the href attribute is not present.

The activation behavior of area elements is to run the following steps:

  1. If the DOMActivate event in question is not trusted (i.e. a click() method call was the reason for the event being dispatched), and the area element's target attribute is ... then raise an INVALID_ACCESS_ERR exception.
  2. Otherwise, the user agent must follow the hyperlink defined by the area element, if any.

One way that a user agent can enable users to follow hyperlinks is by allowing area elements to be clicked, or focussed and activated by the keyboard. This will cause the aforementioned activation behavior to be invoked.

The DOM attributes alt, coords, href, target, ping, rel, media, hreflang, and type, each must reflect the respective content attributes of the same name.

The DOM attribute shape must reflect the shape content attribute, limited to only known values.

The DOM attribute relList must reflect the rel content attribute.

3.12.14 Image maps

An image map allows geometric areas on an image to be associated with hyperlinks.

An image, in the form of an img element or an object element representing an image, may be associated with an image map (in the form of a map element) by specifying a usemap attribute on the img or object element. The usemap attribute, if specified, must be a valid hash-name reference to a map element.

If an img element or an object element representing an image has a usemap attribute specified, user agents must process it as follows:

  1. First, rules for parsing a hash-name reference to a map element must be followed. This will return either an element (the map) or null.

  2. If that returned null, then abort these steps. The image is not associated with an image map after all.

  3. Otherwise, the user agent must collect all the area elements that are descendants of the map. Let those be the areas.

Having obtained the list of area elements that form the image map (the areas), interactive user agents must process the list in one of two ways.

If the user agent intends to show the text that the img element represents, then it must use the following steps.

In user agents that do not support images, or that have images disabled, object elements cannot represent images, and thus this section never applies (the fallback content is shown instead). The following steps therefore only apply to img elements.

  1. Remove all the area elements in areas that have no href attribute.

  2. Remove all the area elements in areas that have no alt attribute, or whose alt attribute's value is the empty string, if there is another area element in areas with the same value in the href attribute and with a non-empty alt attribute.

  3. Each remaining area element in areas represents a hyperlink. Those hyperlinks should all be made available to the user in a manner associated with the text of the img.

    In this context, user agents may represent area and img elements with no specified alt attributes, or whose alt attributes are the empty string or some other non-visible text, in a user-agent-defined fashion intended to indicate the lack of suitable author-provided text.

If the user agent intends to show the image and allow interaction with the image to select hyperlinks, then the image must be associated with a set of layered shapes, taken from the area elements in areas, in reverse tree order (so the last specified area element in the map is the bottom-most shape, and the first element in the map, in tree order, is the top-most shape).

Each area element in areas must be processed as follows to obtain a shape to layer onto the image:

  1. Find the state that the element's shape attribute represents.

  2. Use the rules for parsing a list of integers to parse the element's coords attribute, if it is present, and let the result be the coords list. If the attribute is absent, let the coords list be the empty list.

  3. If the number of items in the coords list is less than the minimum number given for the area element's current state, as per the following table, then the shape is empty; abort these steps.

    State Minimum number of items
    Circle state 3
    Default state 0
    Polygon state 6
    Rectangle state 4
  4. Check for excess items in the coords list as per the entry in the following list corresponding to the shape attribute's state:

    Circle state
    Drop any items in the list beyond the third.
    Default state
    Drop all items in the list.
    Polygon state
    Drop the last item if there's an odd number of items.
    Rectangle state
    Drop any items in the list beyond the fourth.
  5. If the shape attribute represents the rectangle state, and the first number in the list is numerically less than the third number in the list, then swap those two numbers around.

  6. If the shape attribute represents the rectangle state, and the second number in the list is numerically less than the fourth number in the list, then swap those two numbers around.

  7. If the shape attribute represents the circle state, and the third number in the list is less than or equal to zero, then the shape is empty; abort these steps.

  8. Now, the shape represented by the element is the one described for the entry in the list below corresponding to the state of the shape attribute:

    Circle state

    Let x be the first number in coords, y be the second number, and r be the third number.

    The shape is a circle whose center is x CSS pixels from the left edge of the image and x CSS pixels from the top edge of the image, and whose radius is r pixels.

    Default state

    The shape is a rectangle that exactly covers the entire image.

    Polygon state

    Let xi be the (2i)th entry in coords, and yi be the (2i+1)th entry in coords (the first entry in coords being the one with index 0).

    Let the coordinates be (xi, yi), interpreted in CSS pixels measured from the top left of the image, for all integer values of i from 0 to (N/2)-1, where N is the number of items in coords.

    The shape is a polygon whose vertices are given by the coordinates, and whose interior is established using the even-odd rule. [GRAPHICS]

    Rectangle state

    Let x1 be the first number in coords, y1 be the second number, x2 be the third number, and y2 be the fourth number.

    The shape is a rectangle whose top-left corner is given by the coordinate (x1, y1) and whose bottom right corner is given by the coordinate (x2, y2), those coordinates being interpreted as CSS pixels from the top left corner of the image.

    For historical reasons, the coordinates must be interpreted relative to the displayed image, even if it stretched using CSS or the image element's width and height attributes.

Mouse clicks on an image associated with a set of layered shapes per the above algorithm must be dispatched to the top-most shape covering the point that the pointing device indicated (if any), and then, must be dispatched again (with a new Event object) to the image element itself. User agents may also allow individual area elements representing hyperlinks to be selected and activated (e.g. using a keyboard); events from this are not also propagated to the image.

Because a map element (and its area elements) can be associated with multiple img and object elements, it is possible for an area element to correspond to multiple focusable areas of the document.

Image maps are live; if the DOM is mutated, then the user agent must act as if it had rerun the algorithms for image maps.

3.12.15 MathML

The math element from the MathML namespace falls into the embedded content category for the purposes of the content models in this specification.

User agents must handle text other than inter-element whitespace found in MathML elements whose content models do not allow raw text by pretending for the purposes of MathML content models, layout, and rendering that that text is actually wrapped in an mtext element in the MathML namespace. (Such text is not, however, conforming.)

User agents must act as if any MathML element whose contents does not match the element's content model was replaced, for the purposes of MathML layout and rendering, by an merror element in the MathML namespace containing some appropriate error message.

To enable authors to use MathML tools that only accept MathML in its XML form, interactive HTML user agents are encouraged to provide a way to export any MathML fragment as a namespace-well-formed XML fragment.

3.12.16 SVG

The svg element from the SVG namespace falls into the embedded content category for the purposes of the content models in this specification.

To enable authors to use SVG tools that only accept SVG in its XML form, interactive HTML user agents are encouraged to provide a way to export any SVG fragment as a namespace-well-formed XML fragment.

3.12.17 Dimension attributes

The width and height attributes on img, embed, object, and video elements may be specified to give the dimensions of the visual content of the element (the width and height respectively, relative to the nominal direction of the output medium), in CSS pixels. The attributes, if specified, must have values that are valid positive non-zero integers.

The specified dimensions given may differ from the dimensions specified in the resource itself, since the resource may have a resolution that differs from the CSS pixel resolution. (On screens, CSS pixels have a resolution of 96ppi, but in general the CSS pixel resolution depends on the reading distance.) If both attributes are specified, then the ratio of the specified width to the specified height must be the same as the ratio of the logical width to the logical height in the resource. The two attributes must be omitted if the resource in question does not have both a logical width and a logical height.

To parse the attributes, user agents must use the rules for parsing dimension values. This will return either an integer length, a percentage value, or nothing. The user agent requirements for processing the values obtained from parsing these attributes are described in the rendering section. If one of these attributes, when parsing, returns no value, it must be treated, for the purposes of those requirements, as if it was not specified.

The width and height DOM attributes on the embed, object, and video elements must reflect the content attributes of the same name.

3.13 Tabular data

3.13.1 Introduction

This section is non-normative.

...examples, how to write tables accessibly, a brief mention of the table model, etc...

3.13.2 The table element

Categories
Flow content.
Contexts in which this element may be used:
Where flow content is expected.
Content model:
In this order: optionally a caption element, followed by either zero or more colgroup elements, followed optionally by a thead element, followed optionally by a tfoot element, followed by either zero or more tbody elements or one or more tr elements, followed optionally by a tfoot element (but there can only be one tfoot element child in total).
Element-specific attributes:
None.
DOM interface:
interface HTMLTableElement : HTMLElement {
           attribute HTMLTableCaptionElement caption;
  HTMLElement createCaption();
  void deleteCaption();
           attribute HTMLTableSectionElement tHead;
  HTMLElement createTHead();
  void deleteTHead();
           attribute HTMLTableSectionElement tFoot;
  HTMLElement createTFoot();
  void deleteTFoot();
  readonly attribute HTMLCollection tBodies;
  HTMLElement createTBody();
  readonly attribute HTMLCollection rows;
  HTMLElement insertRow(in long index);
  void deleteRow(in long index);
};

The table element represents data with more than one dimension (a table).

we need some editorial text on how layout tables are bad practice and non-conforming

The children of a table element must be, in order:

  1. Zero or one caption elements.

  2. Zero or more colgroup elements.

  3. Zero or one thead elements.

  4. Zero or one tfoot elements, if the last element in the table is not a tfoot element.

  5. Either:

  6. Zero or one tfoot element, if there are no other tfoot elements in the table.

The table element takes part in the table model.

The caption DOM attribute must return, on getting, the first caption element child of the table element, if any, or null otherwise. On setting, if the new value is a caption element, the first caption element child of the table element, if any, must be removed, and the new value must be inserted as the first node of the table element. If the new value is not a caption element, then a HIERARCHY_REQUEST_ERR DOM exception must be raised instead.

The createCaption() method must return the first caption element child of the table element, if any; otherwise a new caption element must be created, inserted as the first node of the table element, and then returned.

The deleteCaption() method must remove the first caption element child of the table element, if any.

The tHead DOM attribute must return, on getting, the first thead element child of the table element, if any, or null otherwise. On setting, if the new value is a thead element, the first thead element child of the table element, if any, must be removed, and the new value must be inserted immediately before the first element in the table element that is neither a caption element nor a colgroup element, if any, or at the end of the table otherwise. If the new value is not a thead element, then a HIERARCHY_REQUEST_ERR DOM exception must be raised instead.

The createTHead() method must return the first thead element child of the table element, if any; otherwise a new thead element must be created and inserted immediately before the first element in the table element that is neither a caption element nor a colgroup element, if any, or at the end of the table otherwise, and then that new element must be returned.

The deleteTHead() method must remove the first thead element child of the table element, if any.

The tFoot DOM attribute must return, on getting, the first tfoot element child of the table element, if any, or null otherwise. On setting, if the new value is a tfoot element, the first tfoot element child of the table element, if any, must be removed, and the new value must be inserted immediately before the first element in the table element that is neither a caption element, a colgroup element, nor a thead element, if any, or at the end of the table if there are no such elements. If the new value is not a tfoot element, then a HIERARCHY_REQUEST_ERR DOM exception must be raised instead.

The createTFoot() method must return the first tfoot element child of the table element, if any; otherwise a new tfoot element must be created and inserted immediately before the first element in the table element that is neither a caption element, a colgroup element, nor a thead element, if any, or at the end of the table if there are no such elements, and then that new element must be returned.

The deleteTFoot() method must remove the first tfoot element child of the table element, if any.

The tBodies attribute must return an HTMLCollection rooted at the table node, whose filter matches only tbody elements that are children of the table element.

The createTBody() method must create a new tbody element, insert it immediately after the last tbody element in the table element, if any, or at the end of the table element if the table element has no tbody element children, and then must return the new tbody element.

The rows attribute must return an HTMLCollection rooted at the table node, whose filter matches only tr elements that are either children of the table element, or children of thead, tbody, or tfoot elements that are themselves children of the table element. The elements in the collection must be ordered such that those elements whose parent is a thead are included first, in tree order, followed by those elements whose parent is either a table or tbody element, again in tree order, followed finally by those elements whose parent is a tfoot element, still in tree order.

The behavior of the insertRow(index) method depends on the state of the table. When it is called, the method must act as required by the first item in the following list of conditions that describes the state of the table and the index argument:

If index is less than −1 or greater than the number of elements in rows collection:
The method must raise an INDEX_SIZE_ERR exception.
If the rows collection has zero elements in it, and the table has no tbody elements in it:
The method must create a tbody element, then create a tr element, then append the tr element to the tbody element, then append the tbody element to the table element, and finally return the tr element.
If the rows collection has zero elements in it:
The method must create a tr element, append it to the last tbody element in the table, and return the tr element.
If index is equal to −1 or equal to the number of items in rows collection:
The method must create a tr element, and append it to the parent of the last tr element in the rows collection. Then, the newly created tr element must be returned.
Otherwise:
The method must create a tr element, insert it immediately before the indexth tr element in the rows collection, in the same parent, and finally must return the newly created tr element.

When the deleteRow(index) method is called, the user agent must run the following steps:

  1. If index is equal to −1, then index must be set to the number if items in the rows collection, minus one.

  2. Now, if index is less than zero, or greater than or equal to the number of elements in the rows collection, the method must instead raise an INDEX_SIZE_ERR exception, and these steps must be aborted.

  3. Otherwise, the method must remove the indexth element in the rows collection from its parent.

3.13.3 The caption element

Categories
None.
Contexts in which this element may be used:
As the first element child of a table element.
Content model:
Phrasing content.
Element-specific attributes:
None.
DOM interface:
Uses HTMLElement.

The caption element represents the title of the table that is its parent, if it has a parent and that is a table element.

The caption element takes part in the table model.

3.13.4 The colgroup element

Categories
None.
Contexts in which this element may be used:
As a child of a table element, after any caption elements and before any thead, tbody, tfoot, and tr elements.
Content model:
Zero or more col elements.
Element-specific attributes:
span
DOM interface:
interface HTMLTableColElement : HTMLElement {
           attribute unsigned long span;
};

The colgroup element represents a group of one or more columns in the table that is its parent, if it has a parent and that is a table element.

If the colgroup element contains no col elements, then the element may have a span content attribute specified, whose value must be a valid non-negative integer greater than zero.

The colgroup element and its span attribute take part in the table model.

The span DOM attribute must reflect the content attribute of the same name. The value must be limited to only positive non-zero numbers.

3.13.5 The col element

Categories
None.
Contexts in which this element may be used:
As a child of a colgroup element that doesn't have a span attribute.
Content model:
Empty.
Element-specific attributes:
span
DOM interface:

HTMLTableColElement, same as for colgroup elements. This interface defines one member, span.

If a col element has a parent and that is a colgroup element that itself has a parent that is a table element, then the col element represents one or more columns in the column group represented by that colgroup.

The element may have a span content attribute specified, whose value must be a valid non-negative integer greater than zero.

The col element and its span attribute take part in the table model.

The span DOM attribute must reflect the content attribute of the same name. The value must be limited to only positive non-zero numbers.

3.13.6 The tbody element

Categories
None.
Contexts in which this element may be used:
As a child of a table element, after any caption, colgroup, and thead elements, but only if there are no tr elements that are children of the table element.
Content model:
Zero or more tr elements
Element-specific attributes:
None.
DOM interface:
interface HTMLTableSectionElement : HTMLElement {
  readonly attribute HTMLCollection rows;
  HTMLElement insertRow(in long index);
  void deleteRow(in long index);
};

The HTMLTableSectionElement interface is also used for thead and tfoot elements.

The tbody element represents a block of rows that consist of a body of data for the parent table element, if the tbody element has a parent and it is a table.

The tbody element takes part in the table model.

The rows attribute must return an HTMLCollection rooted at the element, whose filter matches only tr elements that are children of the element.

The insertRow(index) method must, when invoked on an element table section, act as follows:

If index is less than −1 or greater than the number of elements in the rows collection, the method must raise an INDEX_SIZE_ERR exception.

If index is equal to −1 or equal to the number of items in the rows collection, the method must create a tr element, append it to the element table section, and return the newly created tr element.

Otherwise, the method must create a tr element, insert it as a child of the table section element, immediately before the indexth tr element in the rows collection, and finally must return the newly created tr element.

The deleteRow(index) method must remove the indexth element in the rows collection from its parent. If index is less than zero or greater than or equal to the number of elements in the rows collection, the method must instead raise an INDEX_SIZE_ERR exception.

3.13.7 The thead element

Categories
None.
Contexts in which this element may be used:
As a child of a table element, after any caption, and colgroup elements and before any tbody, tfoot, and tr elements, but only if there are no other thead elements that are children of the table element.
Content model:
Zero or more tr elements
Element-specific attributes:
None.
DOM interface:
HTMLTableSectionElement, as defined for tbody elements.

The thead element represents the block of rows that consist of the column labels (headers) for the parent table element, if the thead element has a parent and it is a table.

The thead element takes part in the table model.

3.13.8 The tfoot element

Categories
None.
Contexts in which this element may be used:
As a child of a table element, after any caption, colgroup, and thead elements and before any tbody and tr elements, but only if there are no other tfoot elements that are children of the table element.
As a child of a table element, after any caption, colgroup, thead, tbody, and tr elements, but only if there are no other tfoot elements that are children of the table element.
Content model:
Zero or more tr elements
Element-specific attributes:
None.
DOM interface:
HTMLTableSectionElement, as defined for tbody elements.

The tfoot element represents the block of rows that consist of the column summaries (footers) for the parent table element, if the tfoot element has a parent and it is a table.

The tfoot element takes part in the table model.

3.13.9 The tr element

Categories
None.
Contexts in which this element may be used:
As a child of a thead element.
As a child of a tbody element.
As a child of a tfoot element.
As a child of a table element, after any caption, colgroup, and thead elements, but only if there are no tbody elements that are children of the table element.
Content model:
Zero or more td or th elements
Element-specific attributes:
None.
DOM interface:
interface HTMLTableRowElement : HTMLElement {
  readonly attribute long rowIndex;
  readonly attribute long sectionRowIndex;
  readonly attribute HTMLCollection cells;
  HTMLElement insertCell(in long index);
  void deleteCell(in long index);
};

The tr element represents a row of cells in a table.

The tr element takes part in the table model.

The rowIndex attribute must, if the element has a parent table element, or a parent tbody, thead, or tfoot element and a grandparent table element, return the index of the tr element in that table element's rows collection. If there is no such table element, then the attribute must return −1.

The sectionRowIndex attribute must, if the element has a parent table, tbody, thead, or tfoot element, return the index of the tr element in the parent element's rows collection (for tables, that's the rows collection; for table sections, that's the rows collection). If there is no such parent element, then the attribute must return −1.

The cells attribute must return an HTMLCollection rooted at the tr element, whose filter matches only td and th elements that are children of the tr element.

The insertCell(index) method must act as follows:

If index is less than −1 or greater than the number of elements in the cells collection, the method must raise an INDEX_SIZE_ERR exception.

If index is equal to −1 or equal to the number of items in cells collection, the method must create a td element, append it to the tr element, and return the newly created td element.

Otherwise, the method must create a td element, insert it as a child of the tr element, immediately before the indexth td or th element in the cells collection, and finally must return the newly created td element.

The deleteCell(index) method must remove the indexth element in the cells collection from its parent. If index is less than zero or greater than or equal to the number of elements in the cells collection, the method must instead raise an INDEX_SIZE_ERR exception.

3.13.10 The td element

Categories
Sectioning root.
Contexts in which this element may be used:
As a child of a tr element.
Content model:
Flow content.
Element-specific attributes:
colspan
rowspan
headers
DOM interface:
interface HTMLTableDataCellElement : HTMLTableCellElement {
           attribute DOMString headers;
};

The td element represents a data cell in a table.

The td element may have a headers content attribute specified. The headers attribute, if specified, must contain a string consisting of an unordered set of unique space-separated tokens, each of which must have the value of an ID of a th element taking part in the same table as the td element (as defined by the table model).

The exact effect of the attribute is described in detail in the algorithm for assigning header cells to data cells, which user agents must apply to determine the relationships between data cells and header cells.

The td element and its colspan and rowspan attributes take part in the table model.

The headers DOM attribute must reflect the content attribute of the same name.

3.13.11 The th element

Categories
None.
Contexts in which this element may be used:
As a child of a tr element.
Content model:
Phrasing content.
Element-specific attributes:
colspan
rowspan
scope
DOM interface:
interface HTMLTableHeaderCellElement : HTMLTableCellElement {
           attribute DOMString scope;
};

The th element represents a header cell in a table.

The th element may have a scope content attribute specified. The scope attribute is an enumerated attribute with five states, four of which have explicit keywords:

The row keyword, which maps to the row state
The row state means the header cell applies to all the remaining cells in the row.
The col keyword, which maps to the column state
The column state means the header cell applies to all the remaining cells in the column.
The rowgroup keyword, which maps to the row group state
The row group state means the header cell applies to all the remaining cells in the row group.
The colgroup keyword, which maps to the column group state
The column group state means the header cell applies to all the remaining cells in the column group.
The auto state
The auto state makes the header cell apply to a set of cells selected based on context.

The scope attribute's missing value default is the auto state.

The exact effect of these values is described in detail in the algorithm for assigning header cells to data cells, which user agents must apply to determine the relationships between data cells and header cells.

The th element and its colspan and rowspan attributes take part in the table model.

The scope DOM attribute must reflect the content attribute of the same name.

3.13.12 Attributes common to td and th elements

The td and th elements may have a colspan content attribute specified, whose value must be a valid non-negative integer greater than zero.

The td and th elements may also have a rowspan content attribute specified, whose value must be a valid non-negative integer.

The td and th elements implement interfaces that inherit from the HTMLTableCellElement interface:

interface HTMLTableCellElement : HTMLElement {
           attribute long colSpan;
           attribute long rowSpan;
  readonly attribute long cellIndex;
};

The colSpan DOM attribute must reflect the content attribute of the same name. The value must be limited to only positive non-zero numbers.

The rowSpan DOM attribute must reflect the content attribute of the same name. Its default value, which must be used if parsing the attribute as a non-negative integer returns an error, is also 1.

The cellIndex DOM attribute must, if the element has a parent tr element, return the index of the cell's element in the parent element's cells collection. If there is no such parent element, then the attribute must return 0.

3.13.13 Processing model

The various table elements and their content attributes together define the table model.

A table consists of cells aligned on a two-dimensional grid of slots with coordinates (x, y). The grid is finite, and is either empty or has one or more slots. If the grid has one or more slots, then the x coordinates are always in the range 0 ≤ x < xwidth, and the y coordinates are always in the range 0 ≤ y < yheight. If one or both of xwidth and yheight are zero, then the table is empty (has no slots). Tables correspond to table elements.

A cell is a set of slots anchored at a slot (cellx, celly), and with a particular width and height such that the cell covers all the slots with coordinates (x, y) where cellx ≤ x < cellx+width and celly ≤ y < celly+height. Cells can either be data cells or header cells. Data cells correspond to td elements, and have zero or more associated header cells. Header cells correspond to th elements.

A row is a complete set of slots from x=0 to x=xwidth-1, for a particular value of y. Rows correspond to tr elements.

A column is a complete set of slots from y=0 to y=yheight-1, for a particular value of x. Columns can correspond to col elements, but in the absence of col elements are implied.

A row group is a set of rows anchored at a slot (0, groupy) with a particular height such that the row group covers all the slots with coordinates (x, y) where 0 ≤ x < xwidth and groupy ≤ y < groupy+height. Row groups correspond to tbody, thead, and tfoot elements. Not every row is necessarily in a row group.

A column group is a set of columns anchored at a slot (groupx, 0) with a particular width such that the column group covers all the slots with coordinates (x, y) where groupx ≤ x < groupx+width and 0 ≤ y < yheight. Column groups correspond to colgroup elements. Not every column is necessarily in a column group.

Row groups cannot overlap each other. Similarly, column groups cannot overlap each other.

A cell cannot cover slots that are from two or more row groups. It is, however, possible for a cell to be in multiple column groups. All the slots that form part of one cell are part of zero or one row groups and zero or more column groups.

In addition to cells, columns, rows, row groups, and column groups, tables can have a caption element associated with them. This gives the table a heading, or legend.

A table model error is an error with the data represented by table elements and their descendants. Documents must not have table model errors.

3.13.13.1. Forming a table

To determine which elements correspond to which slots in a table associated with a table element, to determine the dimensions of the table (xwidth and yheight), and to determine if there are any table model errors, user agents must use the following algorithm:

  1. Let xwidth be zero.

  2. Let yheight be zero.

  3. Let pending tfoot elements be a list of tfoot elements, initially empty.

  4. Let the table be the table represented by the table element. The xwidth and yheight variables give the table's dimensions. The table is initially empty.

  5. If the table element has no children elements, then return the table (which will be empty), and abort these steps.

  6. Associate the first caption element child of the table element with the table. If there are no such children, then it has no associated caption element.

  7. Let the current element be the first element child of the table element.

    If a step in this algorithm ever requires the current element to be advanced to the next child of the table when there is no such next child, then the user agent must jump to the step labeled end, near the end of this algorithm.

  8. While the current element is not one of the following elements, advance the current element to the next child of the table:

  9. If the current element is a colgroup, follow these substeps:

    1. Column groups: Process the current element according to the appropriate case below:

      If the current element has any col element children

      Follow these steps:

      1. Let xstart have the value of xwidth.

      2. Let the current column be the first col element child of the colgroup element.

      3. Columns: If the current column col element has a span attribute, then parse its value using the rules for parsing non-negative integers.

        If the result of parsing the value is not an error or zero, then let span be that value.

        Otherwise, if the col element has no span attribute, or if trying to parse the attribute's value resulted in an error, then let span be 1.

      4. Increase xwidth by span.

      5. Let the last span columns in the table correspond to the current column col element.

      6. If current column is not the last col element child of the colgroup element, then let the current column be the next col element child of the colgroup element, and return to the step labeled columns.

      7. Let all the last columns in the table from x=xstart to x=xwidth-1 form a new column group, anchored at the slot (xstart, 0), with width xwidth-xstart, corresponding to the colgroup element.

      If the current element has no col element children
      1. If the colgroup element has a span attribute, then parse its value using the rules for parsing non-negative integers.

        If the result of parsing the value is not an error or zero, then let span be that value.

        Otherwise, if the colgroup element has no span attribute, or if trying to parse the attribute's value resulted in an error, then let span be 1.

      2. Increase xwidth by span.

      3. Let the last span columns in the table form a new column group, anchored at the slot (xwidth-span, 0), with width span, corresponding to the colgroup element.

    2. Advance the current element to the next child of the table.

    3. While the current element is not one of the following elements, advance the current element to the next child of the table:

    4. If the current element is a colgroup element, jump to the step labeled column groups above.

  10. Let ycurrent be zero.

  11. Let the list of downward-growing cells be an empty list.

  12. Rows: While the current element is not one of the following elements, advance the current element to the next child of the table:

  13. If the current element is a tr, then run the algorithm for processing rows, advance the current element to the next child of the table, and return to the step labeled rows.

  14. Run the algorithm for ending a row group.

  15. If the current element is a tfoot, then add that element to the list of pending tfoot elements, advance the current element to the next child of the table, and return to the step labeled rows.

  16. The current element is either a thead or a tbody.

    Run the algorithm for processing row groups.

  17. Advance the current element to the next child of the table.

  18. Return to the step labeled rows.

  19. End: For each tfoot element in the list of pending tfoot elements, in tree order, run the algorithm for processing row groups.

  20. If there exists a row or column in the table the table containing only slots that do not have a cell anchored to them, then this is a table model error.

  21. Return the table.

The algorithm for processing row groups, which is invoked by the set of steps above for processing thead, tbody, and tfoot elements, is:

  1. Let ystart have the value of yheight.

  2. For each tr element that is a child of the element being processed, in tree order, run the algorithm for processing rows.

  3. If yheight > ystart, then let all the last rows in the table from y=ystart to y=yheight-1 form a new row group, anchored at the slot with coordinate (0, ystart), with height yheight-ystart, corresponding to the current element.

  4. Run the algorithm for ending a row group.

The algorithm for ending a row group, which is invoked by the set of steps above when starting and ending a block of rows, is:

  1. While ycurrent is less than yheight, follow these steps:

    1. Run the algorithm for growing downward-growing cells.

    2. Increase ycurrent by 1.

  2. Empty the list of downward-growing cells.

The algorithm for processing rows, which is invoked by the set of steps above for processing tr elements, is:

  1. If yheight is equal to ycurrent, then increase yheight by 1. (ycurrent is never greater than yheight.)

  2. Let xcurrent be 0.

  3. Let current cell be the first td or th element in the tr element being processed.

  4. Run the algorithm for growing downward-growing cells.

  5. Cells: While xcurrent is less than xwidth and the slot with coordinate (xcurrent, ycurrent) already has a cell assigned to it, increase xcurrent by 1.

  6. If xcurrent is equal to xwidth, increase xwidth by 1. (xcurrent is never greater than xwidth.)

  7. If the current cell has a colspan attribute, then parse that attribute's value, and let colspan be the result.

    If parsing that value failed, or returned zero, or if the attribute is absent, then let colspan be 1, instead.

  8. If the current cell has a rowspan attribute, then parse that attribute's value, and let rowspan be the result.

    If parsing that value failed or if the attribute is absent, then let rowspan be 1, instead.

  9. If rowspan is zero, then let cell grows downward be true, and set rowspan to 1. Otherwise, let cell grows downward be false.

  10. If xwidth < xcurrent+colspan, then let xwidth be xcurrent+colspan.

  11. If yheight < ycurrent+rowspan, then let yheight be ycurrent+rowspan.

  12. Let the slots with coordinates (x, y) such that xcurrent ≤ x < xcurrent+colspan and ycurrent ≤ y < ycurrent+rowspan be covered by a new cell c, anchored at (xcurrent, ycurrent), which has width colspan and height rowspan, corresponding to the current cell element.

    If the current cell element is a th element, let this new cell c be a header cell; otherwise, let it be a data cell. To establish what header cells apply to a data cell, use the algorithm for assigning header cells to data cells described in the next section.

    If any of the slots involved already had a cell covering them, then this is a table model error. Those slots now have two cells overlapping.

  13. If cell grows downward is true, then add the tuple {c, xcurrent, colspan} to the list of downward-growing cells.

  14. Increase xcurrent by colspan.

  15. If current cell is the last td or th element in the tr element being processed, then increase ycurrent by 1, abort this set of steps, and return to the algorithm above.

  16. Let current cell be the next td or th element in the tr element being processed.

  17. Return to step 5 (cells).

When the algorithms above require the user agent to run the algorithm for growing downward-growing cells, the user agent must, for each {cell, cellx, width} tuple in the list of downward-growing cells, if any, extend the cell cell so that it also covers the slots with coordinates (x, ycurrent), where cellx ≤ x < cellx+width.

3.13.13.2. Forming relationships between data cells and header cells

Each data cell can be assigned zero or more header cells. The algorithm for assigning header cells to data cells is as follows.

  1. For each header cell in the table, in tree order, run these substeps:

    1. Let (headerx, headery) be the coordinate of the slot to which the header cell is anchored.

    2. Let headerwidth be the width of the header cell.

    3. Let headerheight be the height of the header cell.

    4. Let data cells be a list of data cells, initially empty.

    5. Examine the scope attribute of the th element corresponding to the header cell, and, based on its state, apply the appropriate substep:

      If it is in the row state

      Add all the data cells that cover slots with coordinates (slotx, sloty), where headerx+headerwidth ≤ slotx < xwidth and headery ≤ sloty < headery+headerheight, to the data cells list.

      If it is in the column state

      Add all the data cells that cover slots with coordinates (slotx, sloty), where headerx ≤ slotx < headerx+headerwidth and headery+headerheight ≤ sloty < yheight, to the data cells list.

      If it is in the row group state

      If the header cell is not in a row group, then do nothing.

      Otherwise, let (0, groupy) be the slot at which the row group is anchored, let height be the number of rows in the row group, and add all the data cells that cover slots with coordinates (slotx, sloty), where headerx ≤ slotx < xwidth and headery ≤ sloty < groupy+height, to the data cells list.

      If it is in the column group state

      If the header cell is not anchored in a column group, then do nothing.

      Otherwise, let (groupx, 0) be the slot at which that column group is anchored, let width be the number of columns in the column group, and add all the data cells that cover slots with coordinates (slotx, sloty), where headerx ≤ slotx < groupx+width and headery ≤ sloty < yheight, to the data cells list.

      Otherwise, it is in the auto state

      Run these steps:

      1. If the header cell is equivalent to a wide cell, let headerwidth equal xwidth-headerx. [UNICODE]

      2. Let x equal headerx+headerwidth.

      3. Horizontal: If x is equal to xwidth, then jump down to the step below labeled vertical.

      4. If there is a header cell anchored at (x, headery) with height headerheight, then jump down to the step below labeled vertical.

      5. Add all the data cells that cover slots with coordinates (slotx, sloty), where slotx = x and headery ≤ sloty < headery+headerheight, to the data cells list.

      6. Increase x by 1.

      7. Jump up to the step above labeled horizontal.

      8. Vertical: Let y equal headery+headerheight.

      9. If y is equal to yheight, then jump to the step below labeled end.

      10. If there is a header cell cell anchored at (headerx, y), then follow these substeps:

        1. If the header cell cell is equivalent to a wide cell, then let width be xwidth-headerx. Otherwise, let width be the width of the header cell cell.

        2. If width is equal to headerwidth, then jump to the step below labeled end.

      11. Add all the data cells that cover slots with coordinates (slotx, sloty), where headerx ≤ slotx < headerx+headerwidth and sloty = y, to the data cells list.

      12. Increase y by 1.

      13. Jump up to the step above labeled vertical.

      14. End: Coalesce all the duplicate entries in the data cells list, so that each data cell is only present once, in tree order.

    6. Assign the header cell to all the data cells in the data cells list that correspond to td elements that do not have a headers attribute specified.

  2. For each data cell in the table, in tree order, run these substeps:

    1. If the data cell corresponds to a td element that does not have a headers attribute specified, then skip these substeps and move on to the next data cell (if any).

    2. Otherwise, take the value of the headers attribute and split it on spaces, letting id list be the list of tokens obtained.

    3. For each token in the id list, run the following steps:

      1. Let id be the token.

      2. If there is a header cell in the table whose corresponding th element has an ID that is equal to the value of id, then assign that header cell to the data cell.

A header cell anchored at (headerx, headery) with width headerwidth and height headerheight is said to be equivalent to a wide cell if all the slots with coordinates (slotx, sloty), where headerx+headerwidth ≤ slotx < xwidth and headery ≤ sloty < headery+header