HTML 5

Contexts in which this element may be used:

In a head element containing no other base elements.

Content model:

Empty.

Content attributes:

href

target

DOM interface:

interface HTMLBaseElement : HTMLElement {
           attribute DOMString href;
           attribute DOMString target;
};

The base element allows authors to specify the document base URL for the purposes of resolving relative URLs, and the name of the default browsing context for the purposes of following hyperlinks. The element does not represent any content beyond this information.

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 valid URL.

A base element, if it has an href attribute, must come before any other elements in the tree that have attributes defined as taking URLs, except the html element (its manifest attribute isn't affected by base elements).

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.

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

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

4.2.4 The `link` element

Categories

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.

Content 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(s) is given by the href attribute, which must be present and must contain a valid URL. If the href attribute is absent, then the element does not define a link.

The types of link indicated (the relationships) are 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 values used are 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.

Each link is handled separately. For instance, if there are two link elements with rel="stylesheet", they each count as a separate external resource, and each is affected by its own attributes independently.

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. To obtain the resource, the user agent must resolve the URL given by the href attribute, relative to the element, and then fetch the resulting absolute URL. User agents may opt to only fetch such resources when they are needed, instead of pro-actively fetching all the external resources that are not applied.

The semantics of the protocol used (e.g. HTTP) 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:

The relationship between this document and the resource (given by the rel attribute)
The title of the resource (given by the title attribute).
The address of the resource (given by the href attribute).
The language of the resource (given by the hreflang attribute).
The optimum media for the resource (given by the media attribute).

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 the other relevant conditions apply, and must not apply them otherwise.

The external resource might have further restrictions defined within that limit its applicability. For example, a CSS style sheet might have some @media blocks. This specification does not override such further restrictions or requirements.

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, the type attribute is used as a hint to user agents so that they can avoid fetching resources they do not support. If the attribute is present, then the user agent must assume that the resource is of the given type. If the attribute is omitted, 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 the UA does not support the given MIME type for the given link relationship, then the UA should not fetch the resource; if the UA does support the given MIME type for the given link relationship, then the UA should fetch the resource. If the attribute is omitted, and the external resource link type does not have a default type defined, but the user agent would fetch the resource if the type was known and supported, then the user agent should fetch the resource under the assumption that it will be supported.

User agents must not consider the type attribute authoritative — upon fetching the resource, user agents must not use the type attribute to determine its actual type. Only the actual type (as defined in the next paragraph) is used to determine whether to apply the resource, not the aforementioned assumed type.

If the resource is expected to be an image, user agents may apply the image sniffing rules, with the official type being the type determined from the resource's Content-Type metadata, and use the resulting sniffed type of the resource as if it was the actual type. Otherwise, if the resource is not expected to be an image, or if the user agent opts not to apply those rules, then the user agent must use the resource's Content-Type metadata to determine the type of the resource. If there is no type metadata, but the external resource link type has a default type defined, then the user agent must assume that the resource is of that type.

Once the user agent has established the type of the resource, the user agent must apply the resource if it is of a supported type and the other relevant conditions apply, and must ignore the resource otherwise.

If a document contains 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. (URIs in these headers are to be processed and resolved according to the rules given in HTTP; the rules of this specification don't apply.) [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.

4.2.5 The `meta` element

Categories

Contexts in which this element may be used:

If the charset attribute is present, or if the element is 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 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.

Content 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. There must not be more than one element with a charset attribute per document.

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.

4.2.5.1 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.

4.2.5.2 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 URLs must not be proposed or accepted. Links must be represented using the link element, not the meta element.

4.2.5.3 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. Some of the keywords are non-conforming, as noted in the last column.

State	Keywords	Notes
Content Language	`content-language`	Non-conforming
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:

Content language

This non-conforming pragma sets the document-wide default language. Until the pragma is successfully processed, there is no document-wide default language.

If another meta element in the Content Language 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.
If the meta element has no content attribute, or if that attribute's value is the empty string, then abort these steps.
Let input be the value of the element's content attribute.
Let position point at the first character of input.
Skip whitespace.
Collect a sequence of characters that are neither space characters nor a U+002C COMMA character (",").
Let the document-wide default language be the string that resulted from the previous step.

For meta elements in the Content Language state, the content attribute must have a value consisting of a valid RFC 3066 language code. [RFC3066]

This pragma is not exactly equivalent to the HTTP Content-Language header, for instance it only supports one language. [RFC2616]

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 an ASCII case-insensitive match for 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 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

Refresh state

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.
If the meta element has no content attribute, or if that attribute's value is the empty string, then abort these steps.
Let input be the value of the element's content attribute.
Let position point at the first character of input.
Skip whitespace.
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.
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.
Skip whitespace.
Let url be the address of the current page.
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.
Skip whitespace.
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.
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.
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.
Skip whitespace.
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.
Skip whitespace.
Let url be equal to the substring of input from the character at position to the end of the string.
Strip any trailing space characters from the end of url.
Strip any U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), and U+000D CARRIAGE RETURN (CR) characters from url.
Resolve the url value to an absolute URL, relative to the meta element. If this fails, abort these steps.
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:

just a valid non-negative integer, or
a valid non-negative integer, followed by a U+003B SEMICOLON (;), followed by one or more space characters, followed by either a U+0055 LATIN CAPITAL LETTER U or a U+0075 LATIN SMALL LETTER U, a U+0052 LATIN CAPITAL LETTER R or a U+0072 LATIN SMALL LETTER R, a U+004C LATIN CAPITAL LETTER L or a U+006C LATIN SMALL LETTER L, a U+003D EQUALS SIGN (=), and then a valid URL.

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 URL.

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

4.2.5.4 Other pragma directives

Extensions to the predefined set of pragma directives may, under certain conditions, be registered in the WHATWG Wiki PragmaExtensions page.

Such extensions must use a name that is identical to a previously-registered HTTP header defined in an RFC, and must have behavior identical to that described for the HTTP header. Pragma directions corresponding to headers describing metadata, or not requiring specific user agent processing, must not be registered; instead, use metadata names. Pragma directions corresponding to headers that affect the HTTP processing model (e.g. caching) must not be registered, as they would result in HTTP-level behavior being different for user agents that implement HTML than for user agents that do not.

Anyone is free to edit the WHATWG Wiki PragmaExtensions page at any time to add a pragma directive satisfying these conditions. Such registrations must specify the following information:

Keyword: The actual name being defined.
Brief description: A short description of the purpose of the pragma directive.
Specification: A link to an IETF RFC defining the corresponding HTTP header.

Conformance checkers must use the information given on the WHATWG Wiki PragmaExtensions page to establish if a value not explicitly defined in this specification is allowed or not.

4.2.5.5 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:

The character encoding name given must be the name of the character encoding used to serialize the file.
The value must be a valid character encoding name, and must be the preferred name for that encoding. [IANACHARSET]
The character encoding declaration must be serialized without the use of character references or character escapes of any kind.
The element containing the character encoding declaration must be serialised completely within the first 512 bytes of the document.

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.

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.

4.2.6 The `style` element

Categories

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 other flow content other than other style elements and inter-element whitespace.

Content model:

Depends on the value of the type attribute.

Content 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. The element does not represent content for the user.

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.

The styles might be further limited in scope, e.g. in CSS with the use of @media blocks. This specification does not override such further restrictions or requirements.

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 child nodes of the style element to the style system.

All URLs found by the styling language's processor must be resolved, relative to the element (or as defined by the styling language), when the processor is invoked.

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.

4.2.7 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 fetched, 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 result of resolving the URL given by the element's href content attribute, relative to the element, or the empty string if that fails. 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.

4.3 Scripting

Scripts allow authors to add interactivity to their documents.

Authors are encouraged to use declarative alternatives to scripting where possible, as declarative mechanisms are often more maintainable, and many users disable scripting.

For example, instead of using script to show or hide a section to show more details, the details element could be used.

Authors are also encouraged to make their applications degrade gracefully in the absence of scripting support.

For example, if an author provides a link in a table header to dynamically resort the table, the link could also be made to function without scripts by requesting the sorted table from the server.

4.3.1 The `script` element

Categories

Contexts in which this element may be used:

Where metadata content is expected.

Where phrasing content is expected.

Content model:

If there is no src attribute, depends on the value of the type attribute.

If there is a src attribute, the element must be either empty or contain only script documentation.

Content attributes:

src

async

defer

type

charset

DOM interface:

interface HTMLScriptElement : HTMLElement {
           attribute DOMString src;
           attribute boolean async;
           attribute boolean defer;
           attribute DOMString type;
           attribute DOMString charset;
           attribute DOMString text;
};

The script element allows authors to include dynamic script and data blocks in their documents. The element does not represent content for the user.

When used to include dynamic scripts, the scripts may either be embedded inline or may be imported from an external file using the src attribute. If the language is not that described by "text/javascript", then the type attribute must be present. If the type attribute is present, its value must be the type of the script's language.

When used to include data blocks, the data must be embedded inline, the format of the data must be given using the type attribute, and the src attribute must not be specified.

The type attribute gives the language of the script or format of the data. If the attribute is present, its value must be a valid MIME type, optionally with parameters. The charset parameter must not be specified. (The default, which is used if the attribute is absent, is "text/javascript".) [RFC2046]

The src attribute, if specified, gives the address of the external script resource to use. The value of the attribute must be a valid URL identifying a script resource of the type given by the type attribute, if the attribute is present, or of the type "text/javascript", if the attribute is absent.

The charset attribute gives the character encoding of the external script resource. The attribute must not be specified if the src attribute is not present. If the attribute is set, its value must be a valid character encoding name, must be the preferred name for that encoding, and must match the encoding given in the charset parameter of the Content-Type metadata of the external file, if any. [IANACHARSET]

The async and defer attributes are boolean attributes that indicate how the script should be executed.

There are three possible modes that can be selected using these attributes. If the async attribute is present, then the script will be executed asynchronously, as soon as it is available. If the async attribute is not present but the defer attribute is present, then the script is executed when the page has finished parsing. If neither attribute is present, then the script is fetched and executed immediately, before the user agent continues parsing the page. The exact processing details for these attributes is described below.

The defer attribute may be specified even if the async attribute is specified, to cause legacy Web browsers that only support defer (and not async) to fall back to the defer behavior instead of the synchronous blocking behavior that is the default.

Changing the src, type, charset, async, and defer attributes dynamically has no direct effect; these attribute are only used at specific times described below (namely, when the element is inserted into the document).

script elements have four associated pieces of metadata. The first is a flag indicating whether or not the script block has been "already executed". Initially, script elements must have this flag unset (script blocks, when created, are not "already executed"). When a script element is cloned, the "already executed" flag, if set, must be propagated to the clone when it is created. The second is a flag indicating whether the element was "parser-inserted". This flag is set by the HTML parser and is used to handle document.write() calls. The third and fourth pieces of metadata are the script block's type and the script block's character encoding. They are determined when the script is run, based on the attributes on the element at that time.

When a script element that is neither marked as having "already executed" nor marked as being "parser-inserted" experiences one of the events listed in the following list, the user agent must run the script element:

The script element gets inserted into a document.
The script element's child nodes are changed.
The script element has a src attribute set where previously the elment had no such attribute.

Running a script: When a script element is to be run, the user agent must act as follows:

If either:
- the script element has a type attribute and its value is the empty string, or
- the script element has no type attribute but it has a language attribute and that attribute's value is the empty string, or
- the script element has neither a type attribute nor a language attribute, then
...let the script block's type for this script element be "text/javascript".

Otherwise, if the script element has a type attribute, let the script block's type for this script element be the value of that attribute.

Otherwise, the element has a non-empty language attribute; let the script block's type for this script element be the concatenation of the string "text/" followed by the value of the language attribute.

The language attribute is never conforming, and is always ignored if there is a type attribute present.
If the script element has a charset attribute, then let the script block's character encoding for this script element be the encoding given by the charset attribute.

Otherwise, let the script block's character encoding for this script element be the same as the encoding of the document itself.
If scripting is disabled for the script element, or if the user agent does not support the scripting language given by the script block's type for this script element, then the user agent must abort these steps at this point. The script is not executed.
If the element has no src attribute, and its child nodes consist only of comment nodes and empty text nodes, then the user agent must abort these steps at this point. The script is not executed.
The user agent must set the element's "already executed" flag.
If the element has a src attribute, then the value of that attribute must be resolved relative to the element, and if that is successful, the specified resource must then be fetched.

For historical reasons, if the URL is a javascript: URL, then the user agent must not, despite the requirements in the definition of the fetching algorithm, actually execute the given script; instead the user agent must act as if it had received an empty HTTP 400 response.

Once the resource's Content Type metadata is available, if it ever is, apply the algorithm for extracting an encoding from a Content-Type to it. If this returns an encoding, and the user agent supports that encoding, then let the script block's character encoding be that encoding.

Once the fetching process has completed, and the script has completed loading, the user agent will have to complete the steps described below. (If the parser is still active at that time, those steps defer to the parser to handle the execution of pending scripts.)

For performance reasons, user agents may start fetching the script as soon as the attribute is set, instead, in the hope that the element will be inserted into the document. Either way, once the element is inserted into the document, the load must have started. If the UA performs such prefetching, but the element is never inserted in the document, or the src attribute is dynamically changed, then the user agent will not execute the script, and the fetching process will have been effectively wasted.
Then, the first of the following options that describes the situation must be followed:

If the document is still being parsed, and the element has a defer attribute, and the element does not have an async attribute

The element must be added to the end of the list of scripts that will execute when the document has finished parsing.
This isn't compatible with IE for inline deferred scripts, but then what IE does is pretty hard to pin down exactly. Do we want to keep this like it is? Be more compatible?

If the element has an async attribute and a src attribute

The element must be added to the end of the list of scripts that will execute asynchronously.

If the element has an async attribute but no src attribute, and the list of scripts that will execute asynchronously is not empty

The element must be added to the end of the list of scripts that will execute asynchronously.

If the element has a src attribute and has been flagged as "parser-inserted"

The element is the pending external script. (There can only be one such script at a time.)

If the element has a src attribute

The element must be added to the end of the list of scripts that will execute as soon as possible.

Otherwise

The user agent must immediately execute the script block, even if other scripts are already executing.

When a script completes loading: If the script element was added to one of the lists mentioned above and the document is still being parsed, then the parser handles it. Otherwise, the UA must run the following steps as the task that the networking task source places on the task queue:

If the script element was added to the list of scripts that will execute when the document has finished parsing:

If the script element is not the first element in the list, then do nothing yet. Stop going through these steps.
Otherwise, execute the script block (the first element in the list).
Remove the script element from the list (i.e. shift out the first entry in the list).
If there are any more entries in the list, and if the script associated with the element that is now the first in the list is already loaded, then jump back to step two to execute it.

If the script element was added to the list of scripts that will execute asynchronously:

If the script is not the first element in the list, then do nothing yet. Stop going through these steps.
Execute the script block (the first element in the list).
Remove the script element from the list (i.e. shift out the first entry in the list).
If there are any more scripts in the list, and the element now at the head of the list had no src attribute when it was added to the list, or had one, but its associated script has finished loading, then jump back to step two to execute the script associated with this element.

If the script element was added to the list of scripts that will execute as soon as possible:

Execute the script block.
Remove the script element from the list.

Fetching an external script must delay the load event.

Executing a script block: When the steps above require that the script block be executed, the user agent must act as follows:

If the load resulted in an error (for example a DNS error, or an HTTP 404 error)

Executing the script block must just consist of firing an error event at the element.

If the load was successful

Initialize the script block's source as follows:

If the script is from an external file

The contents of that file, interpreted as string of Unicode characters, are the script source.

The file must be converted to Unicode using the character encoding given by the script block's character encoding.

If the script is inline and the script block's type is a text-based language

The value of the DOM text attribute at the time the "running a script" algorithm was first invoked is the script source.

If the script is inline and the script block's type is an XML-based language

The child nodes of the script element at the time the "running a script" algorithm was first invoked are the script source.
Create a script from the script element node, using the the script block's source and the the script block's type.

This is where the script is compiled and actually executed.
Fire a load event at the script element.

The DOM attributes src, type, charset, async, and defer, each must reflect the respective content attributes of the same name.

The DOM attribute text must return a concatenation of the contents of all the text nodes that are direct children of the script element (ignoring any other nodes such as comments or elements), in tree order. On setting, it must act the same way as the textContent DOM attribute.

In this example, two script elements are used. One embeds an external script, and the other includes some data.

<script src="game-engine.js"></script>
<script type="text/x-game-map">
........U.........e
o............A....e
.....A.....AAA....e
.A..AAA...AAAAA...e
</script>

The data in this case might be used by the script to generate the map of a video game. The data doesn't have to be used that way, though; maybe the map data is actually embedded in other parts of the page's markup, and the data block here is just used by the site's search engine to help users who are looking for particular features in their game maps.

When inserted using the document.write() method, script elements execute (typically synchronously), but when inserted using innerHTML and outerHTML attributes, they do not execute at all.

4.3.1.1 Scripting languages

A user agent is said to support the scripting language if the script block's type matches the MIME type of a scripting language that the user agent implements.

The following lists some MIME types and the languages to which they refer:

text/javascript
text/javascript1.1
text/javascript1.2
text/javascript1.3: ECMAScript. [ECMA262]
text/javascript;e4x=1: ECMAScript with ECMAScript for XML. [ECMA357]

User agents may support other MIME types and other languages.

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.

4.3.1.2 Inline documentation for external scripts

If a script element's src attribute is specified, then the contents of the script element, if any, must be such that the value of the DOM text attribute, which is derived from the element's contents, matches the documentation production in the following ABNF, the character set for which is Unicode. [ABNF]

documentation = *( *( space / tab / comment ) [ line-comment ] newline )
comment       = slash star *( not-star / star not-slash ) 1*star slash
line-comment  = slash slash *not-newline

; characters
tab           = %x0009 ; U+0009 TAB
newline       = %x000A ; U+000A LINE FEED
space         = %x0020 ; U+0020 SPACE
star          = %x002A ; U+002A ASTERISK
slash         = %x002F ; U+002F SOLIDUS
not-newline   = %x0000-0009 / %x000B-%10FFFF
                ; a Unicode character other than U+000A LINE FEED
not-star      = %x0000-0029 / %x002B-%10FFFF
                ; a Unicode character other than U+002A ASTERISK
not-slash     = %x0000-002E / %x0030-%10FFFF
                ; a Unicode character other than U+002F SOLIDUS

This allows authors to include documentation, such as license information or API information, inside their documents while still referring to external script files. The syntax is constrained so that authors don't accidentally include what looks like valid script while also providing a src attribute.

<script src="cool-effects.js">
 // create new instances using:
 //    var e = new Effect();
 // start the effect using .play, stop using .stop:
 //    e.play();
 //    e.stop();
</script>

4.3.2 The `noscript` element

Categories: Metadata content.; Flow content.; Phrasing content.
Contexts in which this element may be used:: In a head element of an HTML document, if there are no ancestor noscript elements.; Where phrasing content is expected in HTML documents, if there are no ancestor noscript elements.
Content model:: When scripting is disabled, in a head element: in any order, zero or more link elements, zero or more style elements, and zero or more meta elements.; When scripting is disabled, not in a head element: transparent, but there must be no noscript element descendants.; Otherwise: text that conforms to the requirements given in the prose.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The noscript element represents nothing if scripting is enabled, and represents its children if scripting is disabled. It is used to present different markup to user agents that support scripting and those that don't support scripting, by affecting how the document is parsed.

When used in HTML documents, the allowed content model is as follows:

In a head element, if scripting is disabled for the noscript element

The noscript element must contain only link, style, and meta elements.

In a head element, if scripting is enabled for the noscript element

The noscript element must contain only text, except that invoking the HTML fragment parsing algorithm with the noscript element as the context element and the text contents as the input must result in a list of nodes that consists only of link, style, and meta elements, and no parse errors.

Outside of head elements, if scripting is disabled for the noscript element

The noscript element's content model is transparent, with the additional restriction that a noscript element must not have a noscript element as an ancestor (that is, noscript can't be nested).

Outside of head elements, if scripting is enabled for the noscript element

The noscript element must contain only text, except that the text must be such that running the following algorithm results in a conforming document with no noscript elements and no script elements, and such that no step in the algorithm causes an HTML parser to flag a parse error:

Remove every script element from the document.
Make a list of every noscript element in the document. For every noscript element in that list, perform the following steps:
1. Let the parent element be the parent element of the noscript element.
2. Take all the children of the parent element that come before the noscript element, and call these elements the before children.
3. Take all the children of the parent element that come after the noscript element, and call these elements the after children.
4. Let s be the concatenation of all the text node children of the noscript element.
5. Set the innerHTML attribute of the parent element to the value of s. (This, as a side-effect, causes the noscript element to be removed from the document.)
6. Insert the before children at the start of the parent element, preserving their original relative order.
7. Insert the after children at the end of the parent element, preserving their original relative order.

All these contortions are required because, for historical reasons, the noscript element is handled differently by the HTML parser based on whether scripting was enabled or not when the parser was invoked. The element is not allowed in XML, because in XML the parser is not affected by such state, and thus the element would not have the desired effect.

The noscript element must not be used in XML documents.

The noscript element is only effective in the HTML serialization, it has no effect in the XML serialization.

The noscript element has no other requirements. In particular, children of the noscript element are not exempt from form submission, scripting, and so forth, even when scripting is enabled for the element.

4.3.3 The `eventsource` element

Categories

Contexts in which this element may be used:

Where metadata content is expected.

Where phrasing content is expected.

Content model:

Empty.

Content attributes:

src

DOM interface:

interface HTMLEventSourceElement : HTMLElement {
           attribute DOMString src;
};

The eventsource element represents a target for events generated by a remote server.

The src attribute, if specified, must give a valid URL identifying a resource that uses the text/event-stream format.

When an eventsource element with a src attribute specified is inserted into the document, and when an eventsource element that is already in the document has a src attribute added, the user agent must run the add declared event source algorithm.

While an eventsource element is in a document, if its src attribute is mutated, the user agent must must run the remove declared event source algorithm followed by the add declared event source algorithm.

When an eventsource element with a src attribute specified is removed from a document, and when an eventsource element that is in a document with a src attribute specified has its src attribute removed, the user agent must run the remove declared event source algorithm.

When it is created, an eventsource element must have its current declared event source set to "undefined".

The add declared event source algorithm is as follows:

Resolve the URL specified by the eventsource element's src attribute, relative to the element.
If that fails, then set the element's current declared event source to "undefined" and abort these steps.
Otherwise, add the resulting absolute URL to the list of event sources for the element.
Let the element's current declared event source be that absolute URL.

The remove declared event source algorithm is as follows:

If the element's current declared event source is "undefined", abort these steps.
Otherwise, remove the element's current declared event source from the list of event sources for the element.
Let the element's current declared event source be "undefined".

There can be more than one eventsource element per document, but authors should take care to avoid opening multiple connections to the same server as HTTP recommends a limit to the number of simultaneous connections that a user agent can open per server.

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

4.4 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.

4.4.1 The `body` element

Categories

Sectioning root.

Contexts in which this element may be used:

As the second element in an html element.

Content model:

Content attributes:

onbeforeunload

onerror

onhashchange

onload

onmessage

onoffline

ononline

onpopstate

onresize

onstorage

onunload

DOM interface:

interface HTMLBodyElement : HTMLElement {
           attribute Function onbeforeunload;
           attribute any      onerror;
           attribute Function onhashchange;
           attribute Function onload;
           attribute Function onmessage;
           attribute Function onoffline;
           attribute Function ononline;
           attribute Function onpopstate;
           attribute Function onresize;
           attribute Function onstorage;
           attribute Function onunload;
};

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.

The body element exposes as event handler content attributes a number of the event handler attributes of the Window object. It also mirrors their event handler DOM attributes.

The onerror and onmessage event handler attributes of the Window object, exposed on the body element, shadow the generic onerror and onmessage event handler attributes normally supported by HTML elements.

Thus, for example, a bubbling message event fired on a child of the body element of a Document would first trigger the onmessage event handler content attributes of that element, then that of the root html element, and only then would it trigger the onmessage event handler content attribute on the body element. This is because the event would bubble from the target, to the body, to the html, to the Document, to the Window, and the event handler attribute on the body is watching the Window not the body. A regular event listener attached to the body using addEventListener(), however, would fire when the event bubbled through the body and not when it reaches the Window object.

4.4.2 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.
Content attributes:: Global attributes
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.

In the following example, we see an article (part of a larger Web page) about apples, containing two short sections.

<article>
 <header>
  <h1>Apples</h1>
  <p>Tasty, delicious fruit!</p>
 </header>
 <p>The apple is the pomaceous fruit of the apple tree.</p>
 <section>
  <h1>Red Delicious</h1>
  <p>These bright red apples are the most common found in many
  supermarkets.</p>
 </section>
 <section>
  <h1>Granny Smith</h1>
  <p>These juicy, green apples and make a great filling for
  apple pies.</p>
 </section>
</article>

4.4.3 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.
Content attributes:: Global attributes
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>

4.4.4 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.
Content attributes:: Global attributes
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.

4.4.5 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.
Content attributes:: Global attributes
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>

...

4.4.6 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.
Content attributes:: Global attributes
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.

4.4.7 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.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The header element represents the header of a section. The element is typically used to group a set of h1–h6 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, the text of header elements is defined to be the text of the highest ranked h1–h6 element descendant of the header element, if there are any such elements, and the first such element if there are multiple elements with that rank. If there are no such elements, then the text of the header element is the empty string.

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.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The footer element represents a 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>
 <header>
  <h1>Lorem ipsum</h1>
  <h2>The ipsum of all lorems</h2>
 </header>
 <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>

4.4.9 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.
Content attributes:: Global attributes
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.

4.4.10 Headings and sections

The h1–h6 elements and the header element are headings.

The first element of heading content in an element of sectioning content represents the header for that section. Subsequent headers of equal or higher rank start new (implied) sections, headers of lower rank start implied subsections that are part of the previous one. In both cases, the element represents the header of the implied section.

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:

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.

4.4.10.1 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. A section is a container that corresponds to some nodes in the original DOM tree. Each section can have one heading associated with it, and can contain any number of further nested sections. 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 following markup fragment:

<body>
 <h1>A</h1>
 <p>B</p>
 <h2>C</h2>
 <p>D</p>
 <h2>E</h2>
 <p>F</p>
</body>

...results in the following outline being created for the body node (and thus the entire document):

Section created for body node.

Associated with heading "A".

Also associated with paragraph "B".

Nested sections:
1. Section implied for first h2 element.
  
  Associated with heading "C".
  
  Also associated with paragraph "D".
  
  No nested sections.
2. Section implied for second h2 element.
  
  Associated with heading "E".
  
  Also associated with paragraph "F".
  
  No nested 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:

Let current outlinee be null. (It holds the element whose outline is being created.)
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.)
Create a stack to hold elements, which is used to handle nesting. Initialize this stack to empty.
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. Finding the deepest child: 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 finding the deepest child.
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 last section of the outline of the current outlinee, 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 new candidate section be the section that contains candidate section in the outline of current outlinee.
4. Let candidate section be new candidate section.
5. Return to step 2.
Push the element being entered onto the stack. (This causes the algorithm to skip any descendants of the element.)

Recall that h1 has the highest rank, and h6 has the lowest rank.
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.
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.
Associate any nodes that were not associated with a section in the steps above with current outlinee as their section.
Associate all nodes with the heading of the section with which they are associated, if any.
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: 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;
    }
  }
}

4.4.10.2 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.

4.5 Grouping content

4.5.1 The `p` element

Categories: Flow content.
Contexts in which this element may be used:: Where flow content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
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>

4.5.2 The `hr` element

Categories: Flow content.
Contexts in which this element may be used:: Where flow content is expected.
Content model:: Empty.
Content attributes:: Global attributes
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.

4.5.3 The `br` element

Categories: Flow content.; Phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Empty.
Content attributes:: Global attributes
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.

4.5.4 The `pre` element

Categories: Flow content.
Contexts in which this element may be used:: Where flow content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
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:

Including an e-mail, with paragraphs indicated by blank lines, lists indicated by lines prefixed with a bullet, and so on.
Including fragments of computer code, with structure indicated according to the conventions of that language.
Displaying ASCII art.

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>

4.5.5 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.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The dialog element represents a conversation, meeting minutes, a chat transcript, a dialog in a screenplay, an instant message log, or some other construct in which different players take turns in discourse.

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.

4.5.6 The `blockquote` element

Categories

Sectioning root.

Contexts in which this element may be used:

Where flow content is expected.

Content model:

Content 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 address, if it has one, should be cited in the cite attribute.

If the cite attribute is present, it must be a valid URL. To obtain the corresponding citation link, the value of the attribute must be resolved relative to the element. User agents should allow users to follow such citation links.

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.

This next example shows the use of cite alongside blockquote:

<p>His next piece was the aptly named <cite>Sonnet 130</cite>:</p>
<blockquote cite="http://quotes.example.org/s/sonnet130.html">
  <p>My mistress' eyes are nothing like the sun,<br>
  Coral is far more red, than her lips red,<br>
  ...

4.5.7 The `ol` element

Categories

Contexts in which this element may be used:

Where flow content is expected.

Content model:

Zero or more li elements.

Content 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>

4.5.8 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.
Content attributes:: Global attributes
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>

4.5.9 The `li` element

Categories

None.

Contexts in which this element may be used:

Inside ol elements.

Inside ul elements.

Inside menu elements.

Content model:

Content attributes:

If the element is a child of an ol element: value

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 Bug's 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 Bug's 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>

If the li element is the child of a menu element and itself has a child that defines a command, then the li element will match the :enabled and :disabled pseudo-classes in the same way as the first such child element does.

4.5.10 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 more dd elements.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The dl element represents 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.

4.5.11 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.
Content attributes:: Global attributes
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>

4.5.12 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.
Content attributes:: Global attributes
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).

A dl can be used to define a vocabulary list, like in a dictionary. In the following example, each entry, given by a dt with a dfn, has several dds, showing the various parts of the definition.

<dl>
 <dt><dfn>happiness</dfn></dt>
 <dd class="pronunciation">/'hæ p. nes/</dd>
 <dd class="part-of-speech"><i><abbr>n.</abbr></i></dd>
 <dd>The state of being happy.</dd>
 <dd>Good fortune; success. <q>Oh <b>happiness</b>! It worked!</q></dd>
 <dt><dfn>rejoice</dfn></dt>
 <dd class="pronunciation">/ri jois'/</dd>
 <dd><i class="part-of-speech"><abbr>v.intr.</abbr></i> To be delighted oneself.</dd>
 <dd><i class="part-of-speech"><abbr>v.tr.</abbr></i> To cause one to be delighted.</dd>
</dl>

4.5.13 Common grouping idioms

4.5.13.1 Tag clouds

This specification does not define any markup specifically for marking up lists of keywords that apply to a group of pages (also known as tag clouds). In general, authors are encouraged to either mark up such lists using ul elements with explicit inline counts that are then hidden and turned into a presentational effect using a style sheet, or to use SVG.

Here, three tags are included in a short tag cloud:

<style>
@media screen, print, handheld, tv {
  /* should be ignored by non-visual browsers */
  .tag-cloud > li > span { display: none; }
  .tag-cloud > li { display: inline; }
  .tag-cloud-1 { font-size: 0.7em; }
  .tag-cloud-2 { font-size: 0.9em; }
  .tag-cloud-3 { font-size: 1.1em; }
  .tag-cloud-4 { font-size: 1.3em; }
  .tag-cloud-5 { font-size: 1.5em; }
}
</style>
...
<ul class="tag-cloud">
 <li class="tag-cloud-4"><a title="28 instances" href="/t/apple">apple</a> <span>(popular)</span>
 <li class="tag-cloud-2"><a title="6 instances"  href="/t/kiwi">kiwi</a> <span>(rare)</span>
 <li class="tag-cloud-5"><a title="41 instances" href="/t/pear">pear</a> <span>(very popular)</span>
</ul>

The actual frequency of each tag is given using the title attribute. A CSS style sheet is provided to convert the markup into a cloud of differently-sized words, but for user agents that do not support CSS or are not visual, the markup contains annotations like "(popular)" or "(rare)" to categorise the various tags by frequency, thus enabling all users to benefit from the information.

The ul element is used (rather than ol) because the order is not particular important: while the list is in fact ordered alphabetically, it would convey the same information if ordered by, say, the length of the tag.

The tag rel-keyword is not used on these a elements because they do not represent tags that apply to the page itself; they are just part of an index listing the tags themselves.

4.6 Text-level semantics

4.6.1 The `a` element

Categories

Interactive content.

When the element only contains phrasing content: phrasing content.

Contexts in which this element may be used:

Where phrasing content is expected.

Content model:

Transparent, but there must be no interactive content descendant.

Content 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 (a hypertext anchor).

If the a element has no href attribute, then the element represents 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 tool bar 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:

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.
If the target of the click 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's left border, if it has one, or the left edge of the image otherwise, to the location of the click, and let y be the distance in CSS pixels from the top edge of the image's top border, if it has one, or the top edge of the image otherwise, 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.
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.

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

The DOM attribute relList must reflect the rel content attribute.

The a element may be wrapped around entire paragraphs, lists, tables, and so forth, even entire sections, so long as there is no interactive content within (e.g. buttons or other links). This example shows how this can be used to make an entire advertising block into a link:

<aside class="advertising">
 <h1>Advertising</h1>
 <a href="http://ad.example.com/?adid=1929&amp;pubid=1422">
  <section>
   <h1>Mellblomatic 9000!</h1>
   <p>Turn all your widgets into mellbloms!</p>
   <p>Only $9.99 plus shipping and handling.</p>
  </section>
 </a>
 <a href="http://ad.example.com/?adid=375&amp;pubid=1422">
  <section>
   <h1>The Mellblom Browser</h1>
   <p>Web browsing at the speed of light.</p>
   <p>No other browser goes faster!</p>
  </section>
 </a>
</aside>

4.6.2 The `q` element

Categories: Flow content.; Phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global 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) must not appear immediately before, after, or inside q elements; they will be inserted into the rendering by the user agent.

Content inside a q element must be quoted from another source, whose address, if it has one, should be cited in the cite attribute. The source may be fictional, as when quoting characters in a novel or screenplay.

The q element must not be used in place of quotation marks that do not represent quotes; for example, it is inappropriate to use the q element for marking up sarcastic statements.

The use of q elements to mark up quotations is entirely optional; using explicit quotation punctuation without q elements is just as correct.

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, quotation marks are used instead of the q element:

<p>His best argument was ❝I disagree❞, which
I thought was laughable.</p>

In the following example, there is no quote — the quotation marks are used to name a word. Use of the q element in this case would be inappropriate.

<p>The word "ineffable" could have been used to describe the disaster
resulting from the campaign's mismanagement.</p>

4.6.3 The `cite` element

Categories: Flow content.; Phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
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>

4.6.4 The `em` element

Categories: Flow content.; Phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
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>

4.6.5 The `strong` element

Categories: Flow content.; Phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
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>

4.6.6 The `small` element

Categories: Flow content.; Phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The small element represents small print (part of a document often describing disclaimers, caveats, or 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 in an article.

<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>

This is distinct from a sidebar, which might be multiple paragraphs long and is removed from the main flow of text. In the following example, we see a sidebar from the same article. This sidebar also has small print, indicating the source of the information in the sidebar.

<aside>
 <h1>Example Corp</h1>
 <p>This company mostly creates small software and Web
 sites.</p>
 <p>The Example Corp company mission is "To provide entertainment
 and news on a sample basis".</p>
 <p><small>Information obtained from <a
 href="http://example.com/about.html">example.com</a> home
 page.</small></p>
</aside>

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>

4.6.7 The `mark` element

Categories: Flow content.; Phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
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.

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>

4.6.8 The `dfn` element

Categories: Flow content.; 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.
Content attributes:: Global attributes; Also, 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>

4.6.9 The `abbr` element

Categories: Flow content.; Phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes; Also, 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>

An alternative way to write this would be:

<p>The <dfn id=whatwg>Web Hypertext Application Technology
Working Group</dfn> (<abbr title="Web Hypertext Application
Technology Working Group">WHATWG</abbr>) 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>

Abbreviations do not have to be marked up using this element. It is expected to be useful in the following cases:

Abbreviations for which the author wants to give expansions, where using the abbr element with a title attribute is an alternative to including the expansion inline (e.g. in parentheses).
Abbreviations that are likely to be unfamiliar to the document's readers, for which authors are encouraged to either mark up the abbreviation using a abbr element with a title attribute or include the expansion inline in the text the first time the abbreviation is used.
Abbreviations whose presence needs to be semantically annotated, e.g. so that they can be identified from a style sheet and given specific styles, for which the abbr element can be used without a title attribute.

Providing an expansion in a title attribute once will not necessarily cause other abbr elements in the same document with the same contents but without a title attribute to behave as if they had the same expansion. Every abbr element is independent.

4.6.10 The `time` element

Categories

Contexts in which this element may be used:

Where phrasing content is expected.

Content model:

Content 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 precise date and/or a time in the proleptic Gregorian calendar. [GREGORIAN]

The datetime attribute, if present, must contain a valid 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 the element's textContent is a valid date or time string in content.

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:

If the datetime attribute is present, then use the rules to parse a date or time string with the flag in attribute from the value of that attribute, and let the result be result.
Otherwise, use the rules to parse a date or time string with the flag in content from the element's textContent, and let the result be result.
If result is empty (because the parsing failed), then the date is unknown, the time is unknown, and the timezone is unknown.
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="2006-09-24T05:00-07:00">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.

The time element is not intended for encoding times for which a precise date or time cannot be established. For example, it would be inappropriate for encoding times like "one millisecond after the big bang", "the early part of the Jurassic period", or "a winter around 250 BCE".

4.6.11 The `progress` element

Categories

Contexts in which this element may be used:

Where phrasing content is expected.

Content model:

Content 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, or 1, otherwise.

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:

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.
Otherwise, it is a determinate progress bar.
If the max attribute is included, then, if a value could be parsed out of it, then the maximum value is that value.
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.
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.
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.
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.
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.
If the maximum value is less than or equal to zero, then it is reset to 1.
If the current value is less than zero, then it is reset to zero.
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 respective 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.

4.6.12 The `meter` element

Categories

Contexts in which this element may be used:

Where phrasing content is expected.

Content model:

Content 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. However, it is also possible to use the attributes to specify these values.

One of the following conditions, along with all the requirements that are listed with that condition, must be met:

There are exactly two numbers in the contents of the element, and the value, min, and max attributes are all omitted

If specified, the low, high, and optimum attributes must have values greater than or equal to zero and less than or equal to the bigger of the two numbers in the contents of the element.

If both the low and high attributes are specified, then the low attribute's value must be less than or equal to the value of the high attribute.

There is exactly one number followed by zero or more White_Space characters and a valid denominator punctuation character in the contents of the element, and the value, min, and max attributes are all omitted

If specified, the low, high, and optimum attributes must have values greater than or equal to zero and less than or equal to the value associated with the denominator punctuation character.

If both the low and high attributes are specified, then the low attribute's value must be less than or equal to the value of the high attribute.

There is exactly one number in the contents of the element, and the value attribute is omitted

There are no numbers in the contents of the element, and the value attribute is specified

If the min attribute attribute is specified, then the minimum is that attribue's value; otherwise, it is 0.

If the max attribute attribute is specified, then the maximum is that attribue's value; otherwise, it is 1.

If there is exactly one number in the contents of the element, then value is that number; otherwise, value is the value of the value attribute.

The following inequalities must hold, as applicable:

minimum ≤ value ≤ maximum
minimum ≤ low ≤ maximum (if low is specified)
minimum ≤ high ≤ maximum (if high is specified)
minimum ≤ optimum ≤ maximum (if optimum is specified)

If both the low and high attributes are specified, then the low attribute's value must be less than or equal to the value of the high attribute.

For the purposes of these requirements, a number is a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), optionally including with a single U+002E FULL STOP character (.), and separated from other numbers by at least one character that isn't any of those; interpreted as a base ten number.

The value, min, low, high, max, and optimum attributes, when present, must have values that are valid floating point numbers.

If no minimum or maximum is specified, then the range is assumed to be 0..1, and the value thus has to be within that range.

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 low boundary is then less than the minimum value, then the low boundary is actually the same as the minimum value. Similarly, if the low boundary is greater than the maximum value, then it is actually the maximum value instead.

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 high boundary is then less than the low boundary, then the high boundary is actually the same as the low boundary. Similarly, if the high boundary is greater than the maximum value, then it is actually the maximum value instead.

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 will result in the following inequalities all being true:

minimum value ≤ actual value ≤ maximum value
minimum value ≤ low boundary ≤ high boundary ≤ maximum value
minimum value ≤ optimum point ≤ maximum value

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 respective 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...

4.6.13 The `code` element

Categories: Flow content.; Phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
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.

4.6.14 The `var` element

Categories: Flow content.; Phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
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>

For mathematics, in particular for anything beyond the simplest of expressions, MathML is more appropriate. However, the var element can still be used to refer to specific variables that are then mentioned in MathML expressions.

In this example, an equation is shown, with a legend that references the variables in the equation. The expression itself is marked up with MathML, but the variables are mentioned in the figure's legend using var.

<figure>
 <math>
  <mi>a</mi>
  <mo>=</mo>
  <msqrt>
   <msup><mi>b</mi><mn>2</mn></msup>
   <mi>+</mi>
   <msup><mi>c</mi><mn>2</mn></msup>
  </msqrt>
 </math>
 <legend> 
  Using Pythagoras' theorem to solve for the hypotenuse <var>a</var> of
  a triangle with sides <var>b</var> and <var>c</var>
 </legend>
</figure>

4.6.15 The `samp` element

Categories: Flow content.; Phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
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>

4.6.16 The `kbd` element

Categories: Flow content.; Phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
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>

4.6.17 The `sub` and `sup` elements

Categories: Flow content.; Phrasing content.
Contexts in which these elements may be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
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>

4.6.18 The `span` element

Categories: Flow content.; Phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
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. It represents its children.

4.6.19 The `i` element

Categories: Flow content.; Phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
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>

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. Similarly, authors are encouraged to consider whether other elements might be more applicable than the i element, for instance the em element for marking up stress emphasis, or the dfn element to mark up the defining instance of a term.

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.

4.6.20 The `b` element

Categories: Flow content.; Phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes
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.

4.6.21 The `bdo` element

Categories: Flow content.; Phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Phrasing content.
Content attributes:: Global attributes; Also, the dir global attribute has special semantics on this element.
DOM interface:: Uses HTMLElement.

The bdo element represents explicit text directionality formatting control for its children. It 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]

4.6.22 The `ruby` element

Categories: Flow content.; 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.
Content attributes:: Global attributes
DOM interface:: Uses HTMLElement.

The ruby element allows one or more spans of phrasing content to be marked with ruby annotations. Ruby annotations are short runs of text presented alongside base text, primarily used in East Asian typography as a guide for pronounciation or to include other annotations. In Japanese, this form of typography is also known as furigana.

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 Japanese text 漢字 is annotated with its kanji reading.

... 
<ruby>
 漢 <rt> かん </rt>
 字 <rt> じ　 </rt>
</ruby>
...

This might be rendered as:

The two main ideographs, each with its kanji annotation rendered in a smaller font above it.

In this example, each ideograph in the traditional Chinese text 漢字 is annotated with its bopomofo reading.

<ruby>
 漢 <rt> ㄏㄢˋ </rt>
 字 <rt> ㄗˋ　 </rt>
</ruby>

This might be rendered as:

The two main ideographs, each with its bopomofo annotation rendered in a smaller font next to it.

In this example, each ideograph in the simplified Chinese text 汉字 is annotated with its pinyin reading.

...
<ruby>
 汉 <rt> hàn </rt>
 字 <rt> zì  </rt>
</ruby>
...

This might be rendered as:

The two main ideographs, each with its pinyin annotation rendered in a smaller font above it.

4.6.23 The `rt` element

Categories: None.
Contexts in which this element may be used:: As a child of a ruby element.
Content model:: Phrasing content.
Content attributes:: Global attributes
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.

4.6.24 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.
Content attributes:: Global attributes
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 its children.

The example above, in which each ideograph in the text 漢字 is annotated with its kanji reading, could be expanded to use rp so that in legacy user agents the readings are in parentheses:

... 
<ruby>
 漢 <rp>(</rp><rt>かん</rt><rp>)</rp>
 字 <rp>(</rp><rt>じ</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:

... 漢 (かん) 字 (じ) ...

4.6.25 Usage summary

We need to summarize the various elements, in particular to distinguish b/i/em/strong/var/q/mark/cite.

4.6.26 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>

4.7 Edits

The ins and del elements represent edits to the document.

4.7.1 The `ins` element

Categories: Flow content.; When the element only contains phrasing content: phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Transparent.
Content attributes:: Global 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>

4.7.2 The `del` element

Categories: Flow content.; When the element only contains phrasing content: phrasing content.
Contexts in which this element may be used:: Where phrasing content is expected.
Content model:: Transparent.
Content attributes:: Global 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.

4.7.3 Attributes common to `ins` and `del` elements

The cite attribute may be used to specify the address of a document 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 valid URL that explains the change. To obtain the corresponding citation link, the value of the attribute must be resolved relative to the element. 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 global date and time string value.

User agents must parse the datetime attribute according to the parse a global date and time string 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 global date and time string). 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.

4.7.4 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.

4.7.5 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="2008-02-12T15:20Z">Bug 225:
 Rain detector doesn't work in snow</ins></li>
 <li><del datetime="2008-03-01T20:22Z"><ins datetime="2008-02-14T12:02Z">Bug 228:
 Water buffer overflows in April</ins></del></li>
 <li><ins datetime="2008-02-16T13:50Z">Bug 230:
 Water heater doesn't use renewable fuels</ins></li>
 <li><del datetime="2008-02-20T21:15Z"><ins datetime="2008-02-16T14:25Z">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>

4.8 Embedded content

4.8.1 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.
Content attributes:: Global attributes
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 B. The <code>Rough Copy</cite> trailer.</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>

4.8.2 The `img` element

Categories

If the element has an usemap attribute: Interactive content.

Contexts in which this element may be used:

Where embedded content is expected.

Content model:

Empty.

Content attributes:

alt

src

usemap

ismap

width

height

DOM interface:

[NamedConstructor=Image(),
 NamedConstructor=Image(in unsigned long width),
 NamedConstructor=Image(in unsigned long width, in unsigned long height)]
interface HTMLImageElement : HTMLElement {
           attribute DOMString alt;
           attribute DOMString src;
           attribute DOMString useMap;
           attribute boolean isMap;
           attribute unsigned long width;
           attribute unsigned long height;
  readonly attribute boolean complete;
};

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.

The src attribute must be present, and must contain a valid URL referencing a non-interactive, optionally animated, image resource that is neither paged nor scripted. If the base URI of the element is the same as the document's address, then the src attribute's value must not be the empty string.

Images can thus be static bitmaps (e.g. PNGs, GIFs, JPEGs), single-page vector documents (single-page PDFs, XML files with an SVG root element), animated bitmaps (APNGs, animated GIFs), animated vector graphics (XML files with an SVG root element that use declarative SMIL animation), and so forth. However, this also precludes SVG files with script, multipage PDF files, interactive MNG files, HTML documents, plain text documents, and so forth.

The requirements on the alt attribute's value are described in the next section.

There has been some suggestion that the longdesc attribute from HTML4 should be included. This has been considered and rejected in the past, but if new evidence is found showing the attribute to actually help users rather than harm them, it may be reconsidered.

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.

Unless the user agent cannot support images, or its support for images has been disabled, or the user agent only fetches elements on demand, or the element's src attribute has a value that is an ignored self-reference, then, when an img is created with a src attribute, and whenever the src attribute is set subsequently, the user agent must resolve the value of that attribute, relative to the element, and if that is successful must then fetch that resource.

The src attribute's value is an ignored self-reference if its value is the empty string, and the base URI of the element is the same as the document's address.

Fetching 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.

If the image's type is a supported image type, and the image is a valid image of that type, then the image is said to be available (this affects exactly what the element represents, as defined below). This can be true even before the image is completely downloaded, if the user agent supports incremental rendering of images; in such cases, each task that is queued by the networking task source while the image is being fetched must update the presentation of the image appropriately.

If the image was not fetched (e.g. because the UA's image support is disabled, or because the src attribute's value is an ignored self-reference), or if the conditions in the previous paragraph are not met, then the image is not available.

An image might be available in one view but not another. For instance, a Document could be rendered by a screen reader providing a speech synthesis view of the output of a Web browser using the screen media. In this case, the image would be available in the Web browser's screen view, but not available in the screen reader's view.

Whether the image is fetched successfully or not (e.g. whether the response code was a 2xx code or equivalent) must be ignored when determining the image's type and whether it is a valid image.

This allows servers to return images with error responses, and have them displayed.

The user agents should apply the image sniffing rules to determine the type of the image, with the image's associated Content-Type headers giving the official type. If these rules are not applied, then the type of the image must be the type given by the image's associated Content-Type headers.

User agents must not support non-image resources with the img element (e.g. XML files whose root element is an HTML element). User agents must not run executable code (e.g. scripts) embedded in the image resource. User agents must only display the first page of a multipage resource (e.g. a PDF file). User agents must not allow the resource to act in an interactive fashion, but should honour any animation in the resource.

This specification does not specify which image types are to be supported.

The task that is queued by the networking task source once the resource has been fetched, must, if the download was successful and the image is available, queue a task to fire a load event on the img element (this happens after complete starts returning true); and otherwise, if the fetching process fails without a response from the remote server, or completes but the image is not a valid or supported image, queue a task to fire an error event on the img element.

What an img element represents depends on the src attribute and the alt attribute.

If the src attribute is set and the alt attribute is set to the empty string

The image is either decorative or supplemental to the rest of the content, redundant with some other information in the document.

If the image is available and the user agent is configured to display that image, then the element represents the image specified by the src attribute.

Otherwise, the element represents nothing, and may be omitted completely from the rendering. User agents may provide the user with a notification that an image is present but has been omitted from the rendering.

If the src attribute is set and the alt attribute is set to a value that isn't empty

The image is a key part of the content; the alt attribute gives a textual equivalent or replacement for the image.

If the image is available and the user agent is configured to display that image, then the element represents the image specified by the src attribute.

Otherwise, the element represents the text given by the alt attribute. User agents may provide the user with a notification that an image is present but has been omitted from the rendering.

If the src attribute is set and the alt attribute is not

The image might be a key part of the content, and there is no textual equivalent of the image available.

In a conforming document, the absence of the alt attribute indicates that the image is a key part of the content but that a textual replacement for the image was not available when the image was generated.

If the image is available, the element represents the image specified by the src attribute.

If the image is not available or if the user agent is not configured to display the image, then the user agent should display some sort of indicator that there is an image that is not being rendered, and may, if requested by the user, or if so configured, or when required to provide contextual information in response to navigation, provide caption information for the image, derived as follows:

If the image has a title attribute whose value is not the empty string, then the value of that attribute is the caption information; abort these steps.
If the image is the child of a figure element that has a child legend element, then the contents of the first such legend element are the caption information; abort these steps.
Run the algorithm to create the outline for the document.
If the img element did not end up associated with a heading in the outline, or if there are any other images that are lacking an alt attribute and that are associated with the same heading in the outline as the img element in question, then there is no caption information; abort these steps.
The caption information is the heading with which the image is associated according to the outline.

If the src attribute is not set and either the alt attribute is set to the empty string or the alt attribute is not set at all

The element represents nothing.

Otherwise

The element represents the text given by the alt attribute.

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.

User agents may always provide the user with the option to display any image, or to prevent any image from being displayed. User agents may also apply image analysis heuristics to help the user make sense of the image when the user is unable to make direct use of the image, e.g. due to a visual disability or because they are using a text terminal with no graphics capabilities.

The contents of img elements, if any, are ignored for the purposes of rendering.

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 width and height must return the rendered width and height of the image, in CSS pixels, if the image is being rendered, and is being rendered to a visual medium; or else the intrinsic width and height of the image, in CSS pixels, if the image is available but not being rendered to a visual medium; or else 0, if the image is not available or its dimensions are not known. [CSS21]

The DOM attribute complete must return true if the user agent has fetched the image specified in the src attribute, and it is a valid image, even if the final task queued by the networking task source for the fetching of the image resource has not yet been processed. Otherwise, the attribute must return false.

The value of complete can thus change while a script is executing.

Three constructors are provided for creating HTMLImageElement objects (in addition to the factory methods from DOM Core such as createElement()): Image(), Image(width), and Image(width, height). When invoked as constructors, these must return a new HTMLImageElement object (a new img element). If the width argument is present, the new object's width content attribute must be set to width. If the height argument is also present, the new object's height content attribute must be set to height.

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 it is not known at the time of publication what the image will be, only that it will be a coat of arms of some kind, and thus no replacement text can be provided, and instead only a brief caption for the image is provided, in the title attribute:

<p>The last user to have uploaded a coat of arms uploaded this one:</p>
<p><img src="last-uploaded-coat-of-arms.cgi" title="User-uploaded coat of arms."></p>

Ideally, the author would find a way to provide real replacement text even in this case, e.g. by asking the previous user. Not providing replacement text makes the document more difficult to use for people who are unable to view images, e.g. blind users, or users or very low-bandwidth connections or who pay by the byte, or users who are forced to use a text-only Web browser.

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>

4.8.2.1 Requirements for providing text to act as an alternative for images

The requirements for the alt attribute depend on what the image is intended to represent, as described in the following sections.

4.8.2.1.1 A link or button containing nothing but the image

When an a element that is a hyperlink, or a button element, has no textual content but contains one or more images, the alt attributes must contain text that together convey the purpose of the link or button.

In this example, a user is asked to pick his preferred color from a list of three. Each color is given by an image, but for users who have configured their user agent not to display images, the color names are used instead:

<h1>Pick your color</h1>
<ul>
 <li><a href="green.html"><img src="green.jpeg" alt="Green"></a></li>
 <li><a href="blue.html"><img src="blue.jpeg" alt="Blue"></a></li>
 <li><a href="red.html"><img src="red.jpeg" alt="Red"></a></li>
</ul>

In this example, each button has a set of images to indicate the kind of color output desired by the user. The first image is used in each case to give the alternative text.

<button name="rgb"><img src="red" alt="RGB"><img src="green" alt=""><img src="blue" alt=""></button>
<button name="cmyk"><img src="cyan" alt="CMYK"><img src="magenta" alt=""><img src="yellow" alt=""><img src="black" alt=""></button>

Since each image represents one part of the text, it could also be written like this:

<button name="rgb"><img src="red" alt="R"><img src="green" alt="G"><img src="blue" alt="B"></button>
<button name="cmyk"><img src="cyan" alt="C"><img src="magenta" alt="M"><img src="yellow" alt="Y"><img src="black" alt="K"></button>

However, with other alternative text, this might not work, and putting all the alternative text into one image in each case might make more sense:

<button name="rgb"><img src="red" alt="sRGB profile"><img src="green" alt=""><img src="blue" alt=""></button>
<button name="cmyk"><img src="cyan" alt="CMYK profile"><img src="magenta" alt=""><img src="yellow" alt=""><img src="black" alt=""></button>

4.8.2.1.2 A phrase or paragraph with an alternative graphical representation: charts, diagrams, graphs, maps, illustrations

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.

It is important to realize that the alternative text is a replacement for the image, not a description of the image.

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 tokenization 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>

4.8.2.1.3 A short phrase or label with an alternative graphical representation: icons, logos

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, e.g. as a page header, 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.

4.8.2.1.4 Text that has been rendered to a graphic for typographical effect

Sometimes, an image just consists of text, and the purpose of the image is not to highlight the actual typographic effects used to render the text, but just to convey the text itself.

In such cases, the alt attribute must be present but must consist of the same text as written in the image itself.

Consider a graphic containing the text "Earth Day", but with the letters all decorated with flowers and plants. If the text is merely being used as a header, to spice up the page for graphical users, then the correct alternative text is just the same text "Earth Day", and no mention need be made of the decorations:

<h1><img src="earthdayheader.png" alt="Earth Day"></h1>

4.8.2.1.5 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.

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 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>

In these cases, it would be wrong to include alternative text that consists of just a caption. If a caption is to be included, then either the title attribute can be used, or the figure and legend elements can be used. In the latter case, the image would in fact be a phrase or paragraph with an alternative graphical representation, and would thus require alternative text.

<!-- Using the title="" attribute -->
<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=""
        title="Flowchart representation of the parsing model."></p>

<!-- Using <figure> and <legend> -->
<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>
<figure>
 <img src="images/parsing-model-overview.png" alt="The Network leads
 to the Tokeniser, which leads to the Tree Construction. The Tree
 Construction leads to two items. The first is Script Execution, which
 leads via document.write() back to the Tokeniser. The second item
 from which Tree Construction leads is the DOM. The DOM is related to
 the Script Execution.">
 <legend>Flowchart representation of the parsing model.</legend>
</figure>

<!-- This is WRONG. Do not do this. Instead, do what the above examples do. -->
<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="Flowchart representation of the parsing model."></p>
<!-- Never put the image's caption in the alt="" attribute! -->

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>

4.8.2.1.6 A purely decorative image that doesn't add any information

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.

However, a decorative image that isn't discussed by the surrounding text still has some relevance can be included in a page using the img element. 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>

4.8.2.1.7 A group of images that form a single larger picture with no links

When a picture has been sliced into smaller image files that are then displayed together to form the complete picture again, one of the images must have its alt attribute set as per the relevant rules that would be appropriate for the picture as a whole, and then all the remaining images must have their alt attribute set to the empty string.

In the following example, a picture representing a company logo for XYZ Corp has been split into two pieces, the first containing the letters "XYZ" and the second with the word "Corp". The alternative text ("XYZ Corp") is all in the first image.

<h1><img src="logo1.png" alt="XYZ Corp"><img src="logo2.png" alt=""></h1>

In the following example, a rating is shown as three filled stars and two empty stars. While the alternative text could have been "★★★☆☆", the author has instead decided to more helpfully give the rating in the form "3 out of 5". That is the alternative text of the first image, and the rest have blank alternative text.

<p>Rating: <meter max=5 value=3><img src="1" alt="3 out of 5"
  ><img src="1" alt=""><img src="1" alt=""><img src="0" alt=""
  ><img src="0" alt=""></meter></p>

4.8.2.1.8 A group of images that form a single larger picture with links

Generally, image maps should be used instead of slicing an image for links.

However, if an image is indeed sliced and any of the components of the sliced picture are the sole contents of links, then one image per link must have alternative text in its alt attribute representing the purpose of the link.

In the following example, a picture representing the flying spaghetti monster emblem, with each of the left noodly appendages and the right noodly appendages in different images, so that the user can pick the left side or the right side in an adventure.

<h1>The Church</h1>
<p>You come across a flying spaghetti monster. Which side of His
Noodliness do you wish to reach out for?</p>
<p><a href="?go=left" ><img src="fsm-left.png"  alt="Left side. "></a
  ><img src="fsm-middle.png" alt=""
  ><a href="?go=right"><img src="fsm-right.png" alt="Right side."></a></p>

4.8.2.1.9 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.

How to provide alternative text for an image that is a key part of the content depends on the image's provenance.

The general case

When it is possible for detailed 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 can serve as a substitute for the image must be given as the contents of the alt attribute.

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 graph in a financial report:

<img src="sales.gif"
     title="Sales graph"
     alt="From 1998 to 2005, sales increased by the following percentages
     with each year: 624%, 75%, 138%, 40%, 35%, 9%, 21%">

Note that "sales graph" would be inadequate alternative text for a sales graph. Text that would be a good caption is not generally suitable as replacement text.

Images that defy a complete description

In certain cases, the nature of the image might be such that providing thorough alternative text is impractical. For example, the image could be indistinct, or could be a complex fractal, or could be a detailed topographical map.

In these cases, the alt attribute must contain some suitable alternative text, but it may be somewhat brief.

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. However, a description, even if brief, is still better than nothing:

<figure>
 <img src="/commons/a/a7/Rorschach1.jpg" alt="A shape with left-right
 symmetry with indistinct edges, with a small gap in the center, two
 larger gaps offset slightly from the center, with two similar gaps
 under them. The outline is wider in the top half than the bottom
 half, with the sides extending upwards higher than the center, and
 the center extending below the sides.">
 <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.

Another example of an image that defies full description is a fractal, which, by definition, is infinite in complexity.

The following example shows one possible way of providing alternative text for the full view of an image of the Mandelbrot set.

<img src="ms1.jpeg" alt="The Mandelbrot set appears as a cardioid with
its cusp on the real axis in the positive direction, with a smaller
bulb aligned along the same center line, touching it in the negative
direction, and with these two shapes being surrounded by smaller bulbs
of various sizes.">

Images whose contents are not known

In some unfortunate cases, there might be no alternative text available at all, either because the image is obtained in some automated fashion without any associated alternative text (e.g. a Webcam), or because the page is being generated by a script using user-provided images where the user did not provide suitable or usable alternative text (e.g. photograph sharing sites), or because the author does not himself know what the images represent (e.g. a blind photographer sharing an image on his blog).

In such cases, the alt attribute's value may be omitted, but one of the following conditions must be met as well:

The title attribute is present and has a non-empty value.
The img element is in a figure element that contains a legend element that contains content other than inter-element whitespace.
The img element is part of the only paragraph directly in its section, and is the only img element without an alt attribute in its section, and its section has an associated heading.

Such cases are to be kept to an absolute minimum. If there is even the slightest possibility of the author having the ability to provide real alternative text, then it would not be acceptable to omit the alt attribute.

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>

It could also be marked up like this:

<article>
 <h1>Bubbles traveled everywhere with us.</h1>
 <img src="1100670787_6a7c664aef.jpg">
</article>

In either 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.

A blind user's blog in which a photo taken by the user is shown. Initially, the user might not have any idea what the photo he took shows:

<article>
 <h1>I took a photo</h1>
 <p>I went out today and took a photo!</p>
 <figure>
  <img src="photo2.jpeg">
  <legend>A photograph taken blindly from my front porch.</legend>
 </figure>
</article>

Eventually though, the user might obtain a description of the image from his friends and could then include alternative text:

<article>
 <h1>I took a photo</h1>
 <p>I went out today and took a photo!</p>
 <figure>
  <img src="photo2.jpeg" alt="The photograph shows my hummingbird
  feeder hanging from the edge of my roof. It is half full, but there
  are no birds around. In the background, out-of-focus trees fill the
  shot. The feeder is made of wood with a metal grate, and it contains
  peanuts. The edge of the roof is wooden too, and is painted white
  with light blue streaks.">
  <legend>A photograph taken blindly from my front porch.</legend>
 </figure>
</article>

Sometimes the entire point of the image is that a textual description is not available, and the user is to provide the description. For instance, the point of a CAPTCHA image is to see if the user can literally read the graphic. Here is one way to mark up a CAPTCHA (note the title attribute):

<p><label>What does this image say?
<img src="captcha.cgi?id=8934" title="CAPTCHA">
<input type=text name=captcha></label>
(If you cannot see the image, you can use an <a
href="?audio">audio</a> test instead.)</p>

Another example would be software that displays images and asks for alternative text precisely for the purpose of then writing a page with correct alternative text. Such a page could have a table of images, like this:

<table>
 <thead>
  <tr> <th> Image <th> Description
 <tbody>
  <tr>
   <td> <img src="2421.png" title="Image 640 by 100, filename 'banner.gif'">
   <td> <input name="alt2421">
  <tr>
   <td> <img src="2422.png" title="Image 200 by 480, filename 'ad3.gif'">
   <td> <input name="alt2422">
</table>

Notice that even in this example, as much useful information as possible is still included in the title attribute.

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 rather than being provided with replacement text when no alternative text is available and none can be made available, as in the above examples. Lack of effort from the part of the author is not an acceptable reason for omitting the alt attribute.

4.8.2.1.10 An image not intended for the user

Generally authors should avoid using img elements for purposes other than showing images.

If an img element is being used for purposes other than showing an image, e.g. as part of a service to count page views, then the alt attribute must be the empty string.

4.8.2.1.11 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.

4.8.2.1.12 General guidelines

The most general rule for writing alternative text is that the intent is that replacing every image with the text of its alt attribute not change the meaning of the page.

So, in general, alternative text can be written by considering what one would have written had one not been able to include the image.

A corollary to this is that the alt attribute's value should never contain text that could be considered the image's caption, title, or legend. It is supposed to contain replacement text that could be used by users instead of the image; it is not meant to supplement the image. The title attribute can be used for supplemental information.

One way to think of alternative text is to think about how you would read the page containing the image to someone over the phone, without mentioning that there is an image present. Whatever you say instead of the image is typically a good start for writing the alternative text.

4.8.2.1.13 Guidance for markup generators

Markup generators (such as WYSIWYG authoring tools) should, wherever possible, obtain alternative text from their users. However, it is recognised that in many cases, this will not be possible.

For images that are the sole contents of links, markup generators should examine the link target to determine the title of the target, or the URL of the target, and use information obtained in this manner as the alternative text.

As a last resort, implementors should either set the alt attribute to the empty string, under the assumption that the image is a purely decorative image that doesn't add any information but is still specific to the surrounding content, or omit the alt attribute altogther, under the assumption that the image is a key part of the content.

Markup generators should generally avoid using the image's own file name as the alternative text.

4.8.3 The `iframe` element

Categories

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.

Content 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 DOMString width;
           attribute DOMString height;
};

Objects implementing the HTMLIFrameElement interface must also implement the EmbeddingElement interface defined in the Window Object specification. [WINDOW]

The iframe element represents a nested browsing context.

The src attribute gives the address of a page that the nested browsing context is to contain. The attribute, if present, must be a valid URL. When the browsing context is created, if the attribute is present, the user agent must resolve the value of that attribute, relative to the element, and if that is successful, must then navigate the element's browsing context to the resulting absolute URL, 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 WindowProxy object will proxy new Window objects for new Document objects, but the src attribute will not change.

Whenever the src attribute is set, the user agent must resolve the value of that attribute, relative to the element, and if that is successful, the nested browsing context must be navigated to the resulting absolute URL, 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, or if its value cannot be resolved, 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 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 address has the same origin as the iframe element's document, the following requirements apply:

The user agent must set the seamless browsing context flag to true for that browsing context. This will cause links to open in the parent browsing context.
In a CSS-supporting user agent: the user agent must add all the style sheets that apply to the iframe element to the cascade of the active document of the iframe element's nested browsing context, at the appropriate cascade levels, before any style sheets specified by the document itself.
In a CSS-supporting user agent: the user agent must, for the purpose of CSS property inheritance only, treat the root element of the active document of the iframe element's nested browsing context as being a child of the iframe element. (Thus inherited properties on the root element of the document in the iframe will inherit the computed values of those properties on the iframe element instead of taking their initial values.)
In visual media, in a CSS-supporting user agent: the user agent should set the intrinsic width of the iframe to the width that the element would have if it was a non-replaced block-level element with 'width: auto'.
In visual media, in a CSS-supporting user agent: the user agent should set the intrinsic height of the iframe to the height of the bounding box around the content rendered in the iframe at its current width.
In visual media, in a CSS-supporting user agent: the user agent must force the height of the initial containing block of the active document of the nested browsing context of the iframe to zero.

This is intended to get around the otherwise circular dependency of percentage dimensions that depend on the height of the containing block, thus affecting the height of the document's bounding box, thus affecting the height of the viewport, thus affecting the size of the initial containing block.
In speech media, the user agent should render the nested browsing context without announcing that it is a separate document.
User agents should, in general, act as if the active document of the iframe's nested browsing context was part of the document that the iframe is in.

For example if the user agent supports listing all the links in a document, links in "seamlessly" nested documents would be included in that list without being significantly distinguished from links in the document itself.

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 respective content attributes of the same name.

4.8.4 The `embed` element

Categories

Contexts in which this element may be used:

Where embedded content is expected.

Content model:

Empty.

Content 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 DOMString width;
           attribute DOMString 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, if present, must contain a valid URL.

The type attribute, if present, gives the MIME type of the plugin to instantiate. The value must be a valid MIME type, optionally with parameters. If both the type attribute and the src attribute are present, then the type attribute must specify the same type as the explicit Content-Type metadata of the resource given by the src attribute. [RFC2046]

When the element is created with neither a src attribute nor a type attribute, and when attributes are removed such that neither attribute is present on the element anymore, any plugins instantiated for the element must be removed, and the embed element represents nothing.

When 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.

When the element is created with a src attribute, and whenever the src attribute is subsequently set, and whenever the type attribute is set or removed while the element has a src attribute, if the element is not in a sandboxed browsing context, user agents must resolve the value of the attribute, relative to the element, and if that is successful, should fetch the resulting absolute URL, find and instantiate an appropriate plugin based on the content's type, and hand that plugin the content of the resource, replacing any previously instantiated plugin for the element.

Fetching the resource must delay the load event.

The type of the content being embedded is defined as follows:

If the element has a type attribute, and that attribute's value is a type that a plugin supports, then the value of the type attribute is the content's type.
Otherwise, if the <path> component of the URL of the specified resource matches a pattern that a plugin supports, then the content's type is the type that that plugin can handle.

For example, a plugin might say that it can handle resources with <path> components that end with the four character string ".swf".

It would be better if browsers didn't do extension sniffing like this, and only based their decision on the actual contents of the resource. Couldn't we just apply the sniffed type of a resource steps?
Otherwise, if the specified resource has explicit Content-Type metadata, then that is the content's type.
Otherwise, the content has no type and there can be no appropriate plugin for it.

Whether the resource is fetched successfully or not (e.g. whether the response code was a 2xx code or equivalent) must be ignored when determining the resource's type and when handing the resource to the plugin.

This allows servers to return data for plugins even with error responses (e.g. HTTP 500 Internal Server Error codes can still contain plugin data).

When the element is created with a type attribute and no src attribute, and whenever the type attribute is subsequently set, so long as no src attribute is set, and whenever the src attribute is removed when the element has a type attribute, if the element is not in a sandboxed browsing context, user agents should find and instantiate an appropriate plugin based on the value of the type attribute.

Any (namespace-less) attribute may be specified on the embed element, so long as its name is XML-compatible and contains no characters in the range U+0041 .. U+005A (LATIN CAPITAL LETTER A LATIN CAPITAL LETTER Z).

All attributes in HTML documents get lowercased automatically, so the restriction on uppercase letters doesn't affect such documents.

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, when it is instantiated.

If the plugin instantiated for the embed element supports a scriptable interface, the HTMLEmbedElement object representing the element should expose that interface while the element is instantiated.

The embed element has no fallback content. If the user agent can't find a suitable plugin, then the user agent must use a default plugin. (This default could be as simple as saying "Unsupported Format".)

The embed element supports dimension attributes.

The DOM attributes src and type each must reflect the respective content attributes of the same name.

4.8.5 The `object` element

Categories

Listed, submittable, form-associated element.

Contexts in which this element may be used:

Where embedded content is expected.

Content model:

Zero or more param elements, then, transparent.

Content attributes:

data

type

name

usemap

form

width

height

DOM interface:

interface HTMLObjectElement : HTMLElement {
           attribute DOMString data;
           attribute DOMString type;
           attribute DOMString name;
           attribute DOMString useMap;
  readonly attribute HTMLFormElement form;
           attribute DOMString width;
           attribute DOMString 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 valid URL.

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 is removed, or, if the classid attribute is not present, whenever the data attribute changes or is removed, or, if neither classid attribute nor the data attribute are present, whenever the type attribute changes or is removed, the user agent must run the following steps to determine what the object element represents:

If the element has an ancestor object element that is not showing its fallback content, then jump to the last step in the overall set of steps (fallback).
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).
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 fetching the content to examine its real type.
2. Resolve the URL specified by the data attribute, relative to the element.
  
  If that is successful, fetch the resulting absolute URL.
  
  The fetching 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. the URL could not be resolved, there was an HTTP 404 error, there was 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.
    
    Otherwise, if the resource type is "application/octet-stream" but there is no type attribute on the object element, then change the resource type to be unknown, so that the sniffing rules in the next step are invoked.
  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.)
  
  The object element represents the nested browsing context.
  
  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? it could also refetch the resource entirely, maybe from another application cache.
  
  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.
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).
(Fallback.) The object element represents the element's children, 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 attributes on the element, and all the names and values of parameters given by param elements that are children of the object element, in tree order, to the plugin used. If the plugin supports a scriptable interface, the HTMLObjectElement object representing the element should expose that interface. The object element represents the plugin. 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 form attribute is used to explicitly associate the object element with its form owner.

Constraint validation: object elements are always barred from constraint validation.

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>

4.8.6 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.

Content 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. It does not represent anything on its own.

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.

4.8.7 The `video` element

Categories

If the element has a controls attribute: Interactive 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.

Content attributes:

src

poster

autoplay

loop

controls

width

height

DOM interface:

interface HTMLVideoElement : HTMLMediaElement {
           attribute DOMString width;
           attribute DOMString 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, loop, and controls attributes are the attributes common to all media elements.

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 valid URL. If the specified resource is to be used, then, when the element is created or when the poster attribute is set, its value must be resolved relative to the element, and if that is successful, the resulting absolute URL must be fetched. The poster frame is then the image obtained from that resource, if any.

The image given by the poster attribute, the poster frame, is intended to be a representative frame of the video (typically one of the first non-blank frames) that gives the user an idea of what the video is like.

The poster DOM attribute must reflect the poster content attribute.

When no video data is available (the element's readyState attribute is either HAVE_NOTHING or HAVE_METADATA), the video element represents either the poster frame, or nothing.

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 poster frame, at the discretion of the user agent.

Notwithstanding the above, the poster frame should be preferred over nothing, but the poster frame should not be shown again after a frame of video has been shown.

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 potentially 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 neither potentially 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.

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.

The intrinsic width and intrinsic height of the media resource are the dimensions of the resource in CSS pixels after taking into account the resource's dimensions, aspect ratio, clean aperture, resolution, and so forth, as defined for the format used by the resource.

The videoWidth DOM attribute must return the intrinsic width of the video in CSS pixels. The videoHeight DOM attribute must return the intrinsic height of the video in CSS pixels. If the element's readyState attribute is HAVE_NOTHING, then the attributes must return 0.

The video element supports dimension attributes.

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 aspect ratio being preserved. Thus, if the aspect ratio of the playback area does not match the aspect ratio of the video, the video will be shown letterboxed or pillarboxed. Areas of the element's playback area that do not contain the video represent nothing.

The intrinsic width of a video element's playback area is the intrinsic width of the video resource, if that is available; otherwise it is the intrinsic width of the poster frame, if that is available; otherwise it is 300 CSS pixels.

The intrinsic height of a video element's playback area is the intrinsic height of the video resource, if that is available; otherwise it is the intrinsic height of the poster frame, if that is available; otherwise it is 150 CSS pixels.

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.

4.8.7.1 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.

4.8.8 The `audio` element

Categories

If the element has a controls attribute: Interactive 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.

Content attributes:

src

autoplay

loop

controls

DOM interface:

[NamedConstructor=Audio(),
 NamedConstructor=Audio(in DOMString src)]
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, loop, and controls attributes are the attributes common to all media elements.

When an audio element is potentially 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 potentially playing, audio must not play for the element.

Two constructors are provided for creating HTMLAudioElement objects (in addition to the factory methods from DOM Core such as createElement()): Audio() and Audio(src). When invoked as constructors, these must return a new HTMLAudioElement object (a new audio element). If the src argument is present, the object created must have its src content attribute set to the provided value, and the user agent must invoke the load() method on the object before returning.

4.8.8.1 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.

4.8.9 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.

Content attributes: