Differences from HTML4

Abstract

HTML is the core language of the World Wide Web. The W3C publishes HTML5 and HTML5.1. The WHATWG publishes HTML, which is a rough superset of W3C HTML5.1. "Differences from HTML4" describes the differences of the HTML specifications from those of HTML4, and calls out cases where they differ from each other. This document may not provide accurate information, as the specifications are still actively in development. When in doubt, always check the specifications themselves. [HTML5] [HTML5NIGHTLY] [HTML]

Table of Contents

1. 1 Introduction
   1. 1.1 Scope of This Document
   2. 1.2 History of HTML
   3. 1.3 Open Issues
   4. 1.4 Backward Compatibility
   5. 1.5 Development Model
2. 2 Syntax
   1. 2.1 Character Encoding
   2. 2.2 The Doctype
   3. 2.3 MathML and SVG
   4. 2.4 Miscellaneous
3. 3 Language
   1. 3.1 New Elements
   2. 3.2 New Attributes
   3. 3.3 Changed Elements
   4. 3.4 Changed Attributes
   5. 3.5 Obsolete Elements
   6. 3.6 Obsolete Attributes
4. 4 Content Model
5. 5 APIs
   1. 5.1 New APIs
   2. 5.2 Changed APIs
   3. 5.3 Extensions to Document
   4. 5.4 Extensions to HTMLElement
   5. 5.5 Extensions to Other Interfaces
   6. 5.6 Obsolete APIs
6. 6 HTML Changelogs
   1. 6.1 Changes from 14 September 2012 to 6 May 2013
   2. 6.2 Changes from 29 March 2012 to 14 September 2012
   3. 6.3 Changes from 25 May 2011 to 29 March 2012
   4. 6.4 Changes from 5 April 2011 to 25 May 2011
   5. 6.5 Changes from 13 January 2011 to 5 April 2011
   6. 6.6 Changes from 19 October 2010 to 13 January 2011
   7. 6.7 Changes from 24 June 2010 to 19 October 2010
   8. 6.8 Changes from 4 March 2010 to 24 June 2010
   9. 6.9 Changes from 25 August 2009 to 4 March 2010
   10. 6.10 Changes from 23 April 2009 to 25 August 2009
   11. 6.11 Changes from 12 February 2009 to 23 April 2009
   12. 6.12 Changes from 10 June 2008 to 12 February 2009
   13. 6.13 Changes from 22 January 2008 to 10 June 2008
7. Acknowledgments
8. References

1 Introduction

1.1 Scope of This Document

This document covers the W3C HTML5 specification, W3C HTML5.1 specification, and the WHATWG HTML standard. For readability, these are referred to as if they were a single specification: "the HTML specification" or simply "HTML" when something applies equally to all of them; otherwise, they are called out explicitly.

1.2 History of HTML

HTML has been in continuous evolution since it was introduced to the Internet in the early 1990s. Some features were introduced in specifications; others were introduced in software releases. In some respects, implementations and Web developer practices have converged with each other and with specifications and standards, but in other ways, they have diverged.

HTML4 became a W3C Recommendation in 1997. While it continues to serve as a rough guide to many of the core features of HTML, it does not provide enough information to build implementations that interoperate with each other and, more importantly, with Web content. The same goes for XHTML1, which defines an XML serialization for HTML4, and DOM Level 2 HTML, which defines JavaScript APIs for both HTML and XHTML. HTML replaces these documents. [DOM2HTML] [HTML4] [XHTML1]

The HTML specification reflects an effort, started in 2004, to study contemporary HTML implementations and Web content. The specification:

1. Defines a single language called HTML which can be written in HTML syntax and in XML syntax.

2. Defines detailed processing models to foster interoperable implementations.

3. Improves markup for documents.

4. Introduces markup and APIs for emerging idioms, such as Web applications.

1.3 Open Issues

The contents of HTML, as well as the contents of this document which depend on HTML, are still being discussed on the HTML Working Group and WHATWG mailing lists.

Open issues for WHATWG HTML, see "Issues:" at the top of the specification. The specification also has annotation boxes in the margin which can link to bugs.

Open issues for W3C HTML5 and W3C HTML5.1, see the "Status of This Document" section.

1.4 Backward Compatibility

HTML is defined in a way that is backward compatible with the way user agents handle content. To keep the language relatively simple for Web developers, several older elements and attributes are not included, as outlined in the other sections of this document, such as presentational elements that are better handled using CSS.

User agents, however, will always have to support these older elements and attributes. This is why the HTML specification clearly separates requirements for Web developers (referred to as "authors" in the specification) and user agents; for instance, this means that Web developers cannot use the isindex or the plaintext element, but user agents are required to support them in a way that is compatible with how these elements need to behave for compatibility with Web content.

Since HTML has separate conformance requirements for Web developers and user agents there is no longer a need for marking features "deprecated".

1.5 Development Model

The HTML4 specification reached Recommendation status before it was completely implemented in user agents. HTML4 still is not completely implemented, because it contains various bugs that have been fixed in the current HTML specification, which user agents are much closer to implementing than HTML4.

The WHATWG HTML standard is under continual development where bugs are fixed and new features are introduced over time. Features can also be removed from the specification if they lack implementor interest, are not being used by Web developers, or for other reasons. The WHATWG does not publish frozen snapshots.

The W3C HTML5 specification is trying to reach Recommendation status. New features are generally not added unless they are implemented by at least two browsers and have tests demonstrating interoperability. Minor bug fixes can be applied. This means that W3C HTML5 may contain bugs that have been fixed in WHATWG HTML or W3C HTML5.1, or both.

The W3C HTML5.1 specification is similar to WHATWG HTML: it is under continual development where bugs are fixed and new features are introduced over time, and features can be removed from the specification for the same reasons as with WHATWG HTML. It cherry-picks changes from the WHATWG HTML standard and also gets direct changes. It is expected to eventually go through the same procedure as W3C HTML5, and then a new version will be minted.

2 Syntax

HTML defines a syntax, referred to as "the HTML syntax", that is mostly compatible with HTML4 and XHTML1 documents published on the Web, but is not compatible with the more esoteric SGML features of HTML4, such as processing instructions and shorthand markup as these are not supported by most user agents. Documents using the HTML syntax are served with the text/html media type.

HTML also defines detailed parsing rules (including "error handling") for this syntax which are largely compatible with HTML4-era implementations. User agents have to use these rules for resources that have the text/html media type. Here is an example document that conforms to the HTML syntax:

<!doctype html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>Example document</title>
  </head>
  <body>
    <p>Example paragraph</p>
  </body>
</html>

The other syntax that can be used for HTML is XML. This syntax is compatible with XHTML1 documents and implementations. Documents using this syntax need to be served with an XML media type (such as application/xhtml+xml or application/xml) and elements need to be put in the http://www.w3.org/1999/xhtml namespace following the rules set forth by the XML specifications. [XML] [XMLNS]

Below is an example document that conforms to the XML syntax of HTML.

<?xml version="1.0" encoding="UTF-8"?>
<html xmlns="http://www.w3.org/1999/xhtml">
  <head>
    <title>Example document</title>
  </head>
  <body>
    <p>Example paragraph</p>
  </body>
</html>

2.1 Character Encoding

For the HTML syntax, Web developers are required to declare the character encoding. There are three ways to do that:

• At the transport level; for instance, by using the HTTP Content-Type header.

• Using a Unicode Byte Order Mark (BOM) character at the start of the file. This character provides a signature for the encoding used.

• Using a meta element with a charset attribute that specifies the encoding within the first 1024 bytes of the document; for instance, <meta charset="UTF-8"> could be used to specify the UTF-8 encoding. This replaces the need for <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> although that syntax is still allowed.

For the XML syntax, Web developers have to use the rules as set forth in the XML specification to set the character encoding.

2.2 The Doctype

The HTML syntax requires a doctype to be specified to ensure that the browser renders the page in standards mode. The doctype has no other purpose. [DOCTYPE]

The doctype declaration for the HTML syntax is <!DOCTYPE html> and is case-insensitive. Doctypes from earlier versions of HTML were longer because the HTML language was SGML-based and therefore required a reference to a DTD. This is no longer the case and the doctype is only needed to enable standards mode for documents written using the HTML syntax. Browsers already do this for <!DOCTYPE html>.

To support legacy markup generators that cannot generate the preferred short doctype, the doctype <!DOCTYPE html SYSTEM "about:legacy-compat"> is allowed in the HTML syntax.

The strict doctypes for HTML 4.0, HTML 4.01, XHTML 1.0 as well as XHTML 1.1 are also allowed (but are discouraged) in the HTML syntax.

In the XML syntax, any doctype declaration may be used, or it may be omitted altogether. Documents with an XML media type are always handled in standards mode.

2.3 MathML and SVG

The HTML syntax allows for MathML and SVG elements to be used inside a document. An math or svg start tag causes the HTML parser to switch to a special insertion mode which puts elements and attributes in the appropriate namespaces, does case fixups for elements and attributes that have mixed case, and supports the empty-element syntax as in XML. The syntax is still case-insensitive and attributes allow the same syntax as for HTML elements. Namespace declarations may be omitted. CDATA sections are supported in this insertion mode.

Some MathML and SVG elements cause the parser to switch back to "HTML mode", e.g. mtext and foreignObject, so you can use HTML elements or a new math or svg element.

For instance, a very simple document using some of the minimal syntax features could look like:

<!doctype html>
<title>SVG in text/html</title>
<p>
 A green circle:
 <svg> <circle r="50" cx="50" cy="50" fill="green"/> </svg>
</p>

2.4 Miscellaneous

There are a few other changes in the HTML syntax worthy of mentioning:

• The ⟨ and ⟩ named character references now expand to U+27E8 and U+27E9 (mathematical left/right angle bracket) instead of U+2329 and U+232A (left/right-pointing angle bracket), respectively.

• Many new named character references have been added, including all named character references from MathML.

• Void elements (known as "EMPTY" in HTML4) are allowed to have a trailing slash.

• The ampersand (&) may be left unescaped in more cases compared to HTML4.

• Attributes have to be separated by at least one whitespace character.

• Attributes with an empty value may be written as just the attribute name omitting the equals sign and the value, even if the attribute is not a boolean attribute. (It is commonly believed that HTML4 allowed the value to be omitted for boolean attributes. Instead, HTML4 allowed using only the attribute value and omitting the attribute name, for enumerated attributes, but this was not supported in browsers.)

• Attributes omitting quotes for the value are allowed to use a larger set of characters compared to HTML4.

• The HTML parser does not do any normalization of whitespace in attribute values; for instance, leading and trailing whitespace in the id attribute is not ignored (and thus now invalid), and newline characters can be used in the value attribute of the input element without using character references.

• The optgroup end tag is now optional.

• The colgroup start tag is now optional and is inferred by the HTML parser.

3 Language

This section is split up in several subsections to more clearly illustrate the various differences from HTML4.

3.1 New Elements

The following elements have been introduced for better structure:

• section represents a generic document or application section. It can be used together with the h1, h2, h3, h4, h5, and h6 elements to indicate the document structure.

• article represents an independent piece of content of a document, such as a blog entry or newspaper article.

• main can be used as a container for the dominant contents of another element, such as the main content of the page. In W3C HTML5 and W3C HTML 5.1, only one such element is allowed in a document.

• aside represents a piece of content that is only slightly related to the rest of the page.

• In WHATWG HTML, hgroup represents the header of a section.

• header represents a group of introductory or navigational aids.

• footer represents a footer for a section and can contain information about the author, copyright information, etc.

• nav represents a section of the document intended for navigation.

• figure represents a piece of self-contained flow content, typically referenced as a single unit from the main flow of the document.

  <figure>
   <video src="example.webm" controls></video>
   <figcaption>Example</figcaption>
  </figure>

  figcaption can be used as caption (it is optional).

Then there are several other new elements:

• video and audio for multimedia content. Both provide an API so application Web developers can script their own user interface, but there is also a way to trigger a user interface provided by the user agent. source elements are used together with these elements if there are multiple streams available of different types.

• track provides text tracks for the video element.

• embed is used for plugin content.

• mark represents a run of text in one document marked or highlighted for reference purposes, due to its relevance in another context.

• progress represents a completion of a task, such as downloading or when performing a series of expensive operations.

• meter represents a measurement, such as disk usage.

• time represents a date and/or time.

• WHATWG HTML and W3C HTML5.1 has data, which allows content to be annotated with a machine-readable value.

• dialog for showing a dialog.

• ruby, rt, and rp allow for marking up ruby annotations.

• bdi represents a span of text that is to be isolated from its surroundings for the purposes of bidirectional text formatting.

• wbr represents a line break opportunity.

• canvas is used for rendering dynamic bitmap graphics on the fly, such as graphs or games.

• menuitem represents a command the user can invoke from a popup menu.

• details represents additional information or controls which the user can obtain on demand. The summary element provides its summary, legend, or caption.

• datalist together with the a new list attribute for input can be used to make comboboxes:

  <input list="browsers">
  <datalist id="browsers">
   <option value="Safari">
   <option value="Internet Explorer">
   <option value="Opera">
   <option value="Firefox">
  </datalist>

• keygen represents control for key pair generation.

• output represents some type of output, such as from a calculation done through scripting.

The input element's type attribute now has the following new values:

• tel
• search
• url
• email
• datetime
• date
• month
• week
• time
• datetime-local
• number
• range
• color

The idea of these new types is that the user agent can provide the user interface, such as a calendar date picker or integration with the user's address book, and submit a defined format to the server. It gives the user a better experience as his input is checked before sending it to the server meaning there is less time to wait for feedback.

3.2 New Attributes

Several attributes have been introduced to various elements that were already part of HTML4:

• The a and area elements have the new download attribute in WHATWG HTML and W3C HTML5.1. WHATWG HTML also has the ping attribute.

• The area element, for consistency with the a and link elements, now also has the hreflang, type and rel attributes.

• The base element can now have a target attribute as well, mainly for consistency with the a element. (This is already widely supported.)

• The meta element has a charset attribute now as this was already widely supported and provides a nice way to specify the character encoding for the document.

• In WHATWG HTML and W3C HTML5.1, the table element now has a sortable attribute and the th element has a sorted attribute, which provide a means to sort table columns.

• A new autofocus attribute can be specified on the input (except when the type attribute is hidden), select, textarea and button elements. It provides a declarative way to focus a form control during page load. Using this feature should enhance the user experience compared to focusing the element with script as the user can turn it off if the user does not like it, for instance.

• A new placeholder attribute can be specified on the input and textarea elements. It represents a hint intended to aid the user with data entry.

  <input type=email placeholder="a@b.com">

• The new form attribute for input, output, select, textarea, button, label, object and fieldset elements allows for controls to be associated with a form. These elements can now be placed anywhere on a page, not just as descendants of the form element, and still be associated with a form.

  <table>
   <tr>
    <th>Key
    <th>Value
    <th>Action
   <tr>
    <td><form id=1><input name=1-key></form>
    <td><input form=1 name=1-value>
    <td><button form=1 name=1-action value=save>✓</button>
        <button form=1 name=1-action value=delete>✗</button>
   ...
  </table>

• The new required attribute applies to input (except when the type attribute is hidden, image or some button type such as submit), select and textarea. It indicates that the user has to fill in a value in order to submit the form. For select, the first option element has to be a placeholder with an empty value.

  <label>Color: <select name=color required>
   <option value="">Choose one
   <option>Red
   <option>Green
   <option>Blue
  </select></label>

• The fieldset element now allows the disabled attribute which disables all descendant controls (excluding those that are descendants of the legend element) when specified, and the name attribute which can be used for script access.

• The input element has several new attributes to specify constraints: autocomplete, min, max, multiple, pattern and step. As mentioned before it also has a new list attribute which can be used together with the datalist element. It also now has the width and height attributes to specify the dimensions of the image when using type=image.

• The input and textarea elements have a new attribute named dirname that causes the directionality of the control as set by the user to be submitted as well.

• The textarea element also has two new attributes, maxlength and wrap which control max input length and submitted line wrapping behavior, respectively.

• The form element has a novalidate attribute that can be used to disable form validation submission (i.e. the form can always be submitted).

• The input and button elements have formaction, formenctype, formmethod, formnovalidate, and formtarget as new attributes. If present, they override the action, enctype, method, novalidate, and target attributes on the form element.

• In WHATWG HTML and W3C HTML5.1, the input and textarea have an inputmode attribute.

• The menu element has two new attributes: type and label. They allow the element to transform into a menu as found in typical user interfaces as well as providing for context menus in conjunction with the global contextmenu attribute.

• In WHATWG HTML and W3C HTML5.1, the button element has a new menu attribute, used together with popup menus.

• The style element has a new scoped attribute which can be used to enable scoped style sheets. Style rules within such a style element only apply to the local tree.

• The script element has a new attribute called async that influences script loading and execution.

• The html element has a new attribute called manifest that points to an application cache manifest used in conjunction with the API for offline Web applications.

• The link element has a new attribute called sizes. It can be used in conjunction with the icon relationship (set through the rel attribute; can be used for e.g. favicons) to indicate the size of the referenced icon, thus allowing for icons of distinct dimensions.

• The ol element has a new attribute called reversed. When present, it indicates that the list order is descending.

• The iframe element has three new attributes called sandbox, seamless, and srcdoc which allow for sandboxing content, e.g. blog comments.

• The object element has a new attribute called typemustmatch which allows safer embedding of external resources.

• The img element has a new attribute called crossorigin to use CORS in the fetch and if it is successful, allows the image data to be read with the canvas API. In WHATWG HTML and W3C HTML5.1, the script element has a crossorigin attribute to allow script errors to be reported to onerror with information about the error. WHATWG HTML and W3C HTML5.1 also has the crossorigin attribute on the link element.

• In WHATWG HTML, the img element has a new attribute called srcset to support multiple images for different resolutions and different images for different viewport sizes.

Several attributes from HTML4 now apply to all elements. These are called global attributes: accesskey, class, dir, id, lang, style, tabindex and title. Additionally, XHTML 1.0 only allowed xml:space on some elements, which is now allowed on all elements in XHTML documents.

There are also several new global attributes:

• The contenteditable attribute indicates that the element is an editable area. The user can change the contents of the element and manipulate the markup.

• The contextmenu attribute can be used to point to a context menu provided by the Web developer.

• The data-* collection of Web developer-defined attributes. Web developers can define any attribute they want as long as they prefix it with data- to avoid clashes with future versions of HTML. These are intended to be used to store custom data to be consumed by the Web page or application itself. They are not intended for data to be consumed by other parties (e.g. user agents).

• The draggable and dropzone attributes can be used together with the new drag & drop API.

• The hidden attribute indicates that an element is not yet, or is no longer, relevant.

• WHATWG HTML and W3C HTML5.1 has the inert attribute, intended to make dialog elements modal.

• The role and aria-* collection attributes which can be used to instruct assistive technology. These attributes have slightly different requirements in WHATWG HTML and W3C HTML5/W3C HTML5.1.

• The spellcheck attribute allows for hinting whether content can be checked for spelling or not.

• The translate attribute gives a hint to translators whether the content should be translated.

HTML also makes all event handler attributes from HTML4, which take the form onevent, global attributes and adds several new event handler attributes for new events it defines; for instance, the onplay event handler attribute for the play event which is used by the API for the media elements (video and audio).

3.3 Changed Elements

These elements have slightly modified meanings in HTML to better reflect how they are used on the Web or to make them more useful:

• The address element is now scoped by the nearest ancestor article or body element.

• The b element now represents a span of text to which attention is being drawn for utilitarian purposes without conveying any extra importance and with no implication of an alternate voice or mood, such as key words in a document abstract, product names in a review, actionable words in interactive text-driven software, or an article lede.

• The cite element now solely 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, a legal case report, etc). Specifically the example in HTML4 where it is used to mark up the name of a person is no longer considered conforming.

• The dl element now represents an association list of name-value groups, and is no longer said to be appropriate for dialogue.

• The hr element now represents a paragraph-level thematic break.

• The i element now represents a span of text in an alternate voice or mood, or otherwise offset from the normal prose in a manner indicating a different quality of text, such as a taxonomic designation, a technical term, an idiomatic phrase from another language, a thought, or a ship name in Western texts.

• For the label element the browser should no longer move focus from the label to the control unless such behavior is standard for the underlying platform user interface.

• The menu element is redefined to be useful for toolbars and popup menus.

• The noscript element is no longer said to be rendered when the user agent doesn't support a scripting language invoked by a script element earlier in the document.

• The s element now represents contents that are no longer accurate or no longer relevant.

• The script element can now be used for scripts or for custom data blocks.

• The small element now represents side comments such as small print.

• The strong element now represents importance rather than strong emphasis.

• The u element now represents a span of text with an unarticulated, though explicitly rendered, non-textual annotation, such as labeling the text as being a proper name in Chinese text (a Chinese proper name mark), or labeling the text as being misspelt.

3.4 Changed Attributes

Several attributes have changed in various ways.

• The accept attribute on input now allows the values audio/*, video/* and image/*.

• The accesskey global attribute now allows multiple characters to be specified, which the user agent can choose from.

• The action attribute on form is no longer allowed to have an empty URL.

• In WHATWG HTML, the method attribute has a new keyword dialog, intended to close a dialog element.

• The border attribute on table only allows the values "1" and the empty string. In WHATWG HTML, the border attribute is obsolete.

• The colspan attribute on td and th now has to be greater than zero.

• The coords attribute on area no longer allows a percentage value of the radius when the element is in the circle state.

• The data attribute on object is no longer said to be relative to the codebase attribute.

• The defer attribute on script now explicitly makes the script execute when the page has finished parsing.

• The dir global attribute now allows the value auto.

• The enctype attribute on form now supports the value text/plain.

• The width and height attributes on img, iframe and object are no longer allowed to contain percentages. They are also not allowed to be used to stretch the image to a different aspect ratio than its intrinsic aspect ratio.

• The href attribute on link is no longer allowed to have an empty URL.

• The href attribute on base is now allowed to contain a relative URL.

• All attributes that take URLs, e.g. href on the a element, now support IRIs if the document's encoding is UTF-8 or UTF-16.

• The http-equiv attribute on meta is no longer said to be used by HTTP servers to create HTTP headers in the HTTP response. Instead, it is said to be a pragma directive to be used by the user agent.

• The id global attribute is now allowed to have any value, as long as it is unique, is not the empty string, and does not contain space characters.

• The lang global attribute takes the empty string in addition to a valid language identifier, just like xml:lang does in XML.

• The media attribute on link now accepts a media query and defaults to "all".

• The event handler attributes (e.g. onclick) now always use JavaScript as the scripting language.

• The value attribute of the li element is no longer deprecated as it is not presentational. The same goes for the start and type attributes of the ol element.

• The style global attribute now always uses CSS as the styling language.

• The tabindex global attribute now allows negative values which indicate that the element can receive focus but cannot be tabbed to.

• The target attribute of the a and area elements is no longer deprecated, as it is useful in Web applications, e.g. in conjunction with iframe.

• The type attribute on script and style is no longer required if the scripting language is JavaScript and the styling language is CSS, respectively.

• The usemap attribute on img no longer takes a URL, but instead takes a valid hash-name reference to a map element.

The following attributes are allowed but Web developers are discouraged from using them and instead strongly encouraged to use an alternative solution:

• The border attribute on img. It is required to have the value "0" when present. Web developers can use CSS instead.

• The language attribute on script. It is required to have the value "JavaScript" (case-insensitive) when present and cannot conflict with the type attribute. Web developers can simply omit it as it has no useful function.

• The name attribute on a. Web developers can use the id attribute instead.

3.5 Obsolete Elements

The elements in this section are not to be used by Web developers. User agents will still have to support them and various sections in HTML define how. E.g. the obsolete isindex element is handled by the parser section.

The following elements are not in HTML because their effect is purely presentational and their function is better handled by CSS:

• basefont
• big
• center
• font
• strike
• tt

The following elements are not in HTML because using them damages usability and accessibility:

• frame
• frameset
• noframes

The following elements are not included because they have not been used often, created confusion, or their function can be handled by other elements:

• acronym is not included because it has created a lot of confusion. Web developers are to use abbr for abbreviations.

• applet has been obsoleted in favor of object.

• isindex usage can be replaced by usage of form controls.

• dir has been obsoleted in favor of ul.

Finally the noscript element is only conforming in the HTML syntax. It is not allowed in the XML syntax. This is because in order to not only hide visually but also prevent the content to run scripts, apply style sheets, have submittable form controls, load resources, and so forth, the HTML parser parses the content of the noscript element as plain text. The same is not possible with an XML parser.

3.6 Obsolete Attributes

Some attributes from HTML4 are no longer allowed in HTML. The specification defines how user agents should process them in legacy documents, but Web developers are not allowed use them and they will not validate.

HTML has advice on what you can use instead.

• rev and charset attributes on link and a.

• shape and coords attributes on a.

• longdesc attribute on img and iframe.

• target attribute on link.

• nohref attribute on area.

• profile attribute on head.

• version attribute on html.

• name attribute on img (use id instead).

• scheme attribute on meta.

• archive, classid, codebase, codetype, declare and standby attributes on object.

• valuetype and type attributes on param.

• axis attribute on td and th.

• abbr and scope attributes on td.

• summary attribute on table.

In addition, HTML has none of the presentational attributes that were in HTML4 as their functions are better handled by CSS:

• align attribute on caption, iframe, img, input, object, legend, table, hr, div, h1, h2, h3, h4, h5, h6, p, col, colgroup, tbody, td, tfoot, th, thead and tr.

• alink, link, text and vlink attributes on body.

• background attribute on body.

• bgcolor attribute on table, tr, td, th and body.

• border attribute on object.

• cellpadding and cellspacing attributes on table.

• char and charoff attributes on col, colgroup, tbody, td, tfoot, th, thead and tr.

• clear attribute on br.

• compact attribute on dl, menu, ol and ul.

• frame attribute on table.

• frameborder attribute on iframe.

• height attribute on td and th.

• hspace and vspace attributes on img and object.

• marginheight and marginwidth attributes on iframe.

• noshade attribute on hr.

• nowrap attribute on td and th.

• rules attribute on table.

• scrolling attribute on iframe.

• size attribute on hr.

• type attribute on li, and ul.

• valign attribute on col, colgroup, tbody, td, tfoot, th, thead and tr.

• width attribute on hr, table, td, th, col, colgroup and pre.

4 Content Model

The content model is what defines how elements may be nested — what is allowed as children (or descendants) of a certain element.

At a high level, HTML4 had two major categories of elements, "inline" (e.g. span, img, text), and "block-level" (e.g. div, hr, table). Some elements did not fit in either category.

Some elements allowed "inline" elements (e.g. p), some allowed "block-level" elements (e.g. body), some allowed both (e.g. div), while other elements did not allow either category but only allowed other specific elements (e.g. dl, table), or did not allow any children at all (e.g. link, img, hr).

Notice the difference between an element itself being in a certain category, and having a content model of a certain category; for instance, the p element is itself a "block-level" element, but has a content model of "inline".

To make it more confusing, HTML4 had different content model rules in its Strict, Transitional and Frameset flavors; for instance, in Strict, the body element allowed only "block-level" elements, but in Transitional, it allowed both "inline" and "block-level".

To make things more confusing still, CSS uses the terms "block-level element" and "inline-level element" for its visual formatting model, which is related to CSS's 'display' property and has nothing to do with HTML's content model rules.

HTML does not use the terms "block-level" or "inline" as part of its content model rules, to reduce confusion with CSS. However, it has more categories than HTML4, and an element can be part of none of them, one of them, or several of them.

• Metadata content, e.g. link, script.

• Flow content, e.g. span, div, text. This is roughly like HTML4's "block-level" and "inline" together.

• Sectioning content, e.g. aside, section.

• Heading content, e.g. h1.

• Phrasing content, e.g. span, img, text. This is roughly like HTML4's "inline". Elements that are phrasing content are also flow content.

• Embedded content, e.g. img, iframe, svg.

• Interactive content, e.g. a, button, label. Interactive content is not allowed to be nested.

As a broad change from HTML4, HTML no longer has any element that only accepts what HTML4 called "block-level" elements; e.g. the body element now allows flow content. Thus, This is closer to HTML4 Transitional than HTML4 Strict.

Further changes include:

• The address element now allows flow content, but with no heading content descendants, no sectioning content descendants, and no header, footer, or address element descendants.

• HTML4 allowed object in head. HTML does not.

• WHATWG HTML allows link and meta as descendants of body if they use microdata attributes.

• The noscript element was a "block-level" element in HTML4, but is phrasing content in HTML.

• The table, thead, tbody, tfoot, tr, ol, ul and dl elements are allowed to be empty in HTML.

• Table elements have to conform to the table model (e.g. two cells are not allowed to overlap).

• The table element now does not allow col elements as direct children. However, the HTML parser implies a colgroup element, so this change should not affect text/html content.

• The table element now allows the tfoot element to be the last child.

• The caption element now allows flow content, but with no descendant table elements.

• The th element now allows flow content, but with no header, footer, sectioning content, or heading content descendants.

• The a element now has a transparent content model (except it does not allow interactive content descendants), meaning that it has the same content model as its parent. This means that the a element can now contain e.g. div elements, if its parent allows flow content.

• The ins and del elements also have a transparent content model. HTML4 had similar rules in prose that could not be expressed in the DTD.

• The object element also has a transparent content model, after its param children.

• The map element also has a transparent content model. The area element is considered phrasing content if there is a map element ancestor, which means that they do not need to be direct children of map.

• The fieldset element no longer requires a legend child.

5 APIs

HTML has introduced many new APIs and has extended, changed or obsoleted some existing APIs.

5.1 New APIs

HTML introduces a number of APIs that help in creating Web applications. These can be used together with the new elements introduced for applications:

• Media elements (video and audio) have APIs for controlling playback, syncronising multiple media elements, and timed text tracks (e.g. subtitles).

• An API for form constraint validation (e.g. the setCustomValidity() method).

• An API for commands that the user can invoke.

• An API that enables offline Web applications, with an application cache.

• An API that allows a Web application to register itself for certain protocols or media types, using registerProtocolHandler() and registerContentHandler().

• Editing API in combination with a new global contenteditable attribute.

• Drag & drop API in combination with a draggable attribute.

• An API that exposes the components of the document's URL and allows scripts to navigate, redirect and reload (the Location interface).

• An API that exposes the session history and allows scripts to update the document's URL without actually navigating, so that applications don't need to abuse the fragment component for "Ajax-style" navigation (the History interface).

• An API for base64 conversion (atob() and btoa() methods).

• An API to schedule timer-based callbacks (setTimeout() and setInterval()).

• An API to prompt the user (alert(), confirm(), prompt(), showModalDialog()).

• An API for printing the document (print()).

• An API for handling search providers (AddSearchProvider() and IsSearchProviderInstalled()).

• The Window object has been defined.

WHATWG HTML has further APIs that are not in W3C HTML5 but are separate specifications at the W3C:

• An API for microdata.

• An API for immediate-mode bitmap graphics (the 2d context for the canvas element).

• An API for cross-document messaging and channel messaging (postMessage() and MessageChannel).

• An API for runnings scripts in the background (Worker and SharedWorker).

• An API for client-side storage (localStorage and sessionStorage).

• An API for bidirectional client-server communication (WebSocket).

• An API for server-to-client data push (EventSource).

5.2 Changed APIs

The following features from DOM Level 2 HTML are changed in various ways:

• document.title now collapses whitespace on getting.

• document.domain is made settable, which can change the document's effective script origin.

• document.open() now either clears the document (if invoked with two or less arguments), or acts like window.open() (if invoked with three or four arguments). In the former case, throws an exception in XML.

• document.close(), document.write() and document.writeln() throw an exception in XML. The latter two now support variadic arguments; they can add text to the document's input stream while it is still being parsed, imply a call to document.open(), or be ignored altogether in some cases.

• document.getElementsByName() now returns all HTML elements with a name attribute matching the argument.

• elements on HTMLFormElement now returns an HTMLFormControlsCollection of button, fieldset, input, keygen, object, output, select and textarea elements. length returns the number of nodes in elements.

• add() on HTMLSelectElement now also accepts an integer as its second argument.

• remove() on HTMLSelectElement now removes the first element in the collection if the argument is out of bounds.

• a and area elements now stringify to their href attribute.

• The click(), focus() and blur() methods are now available on all HTML elements.

5.3 Extensions to Document

DOM Level 2 HTML had an HTMLDocument interface that inherited from Document and provided HTML-specific members on documents. HTML has moved these members to the Document interface, and extended it in a number of ways. Since all documents use the Document interface, the HTML-specific members are now available on all documents, so they are usable in e.g. SVG documents as well. It also has several new members:

• location, lastModified and readyState to help resource metadata management.

• dir, head, embeds, plugins, scripts, commands, and a generic name getter, to access various parts of the DOM tree.

• WHATWG HTML has getItems() for microdata.

• WHATWG HTML and W3C HTML5.1 have cssElementMap to accompany the CSS element() feature.

• WHATWG HTML and W3C HTML5.1 have currentScript which returns the currently running script element (or null).

• activeElement and hasFocus to determine which element is currently focused and whether the Document has focus respectively.

• designMode, execCommand(), queryCommandEnabled(), queryCommandIndeterm(), queryCommandState(), queryCommandSupported(), queryCommandValue() for the editing API.

• All event handler IDL attributes. Also, onreadystatechange is a special event handler IDL attribute that is only available on Document.

Existing scripts that modified the prototype of HTMLDocument should continue to work because window.HTMLDocument now returns the Document interface object.

5.4 Extensions to HTMLElement

The HTMLElement interface has also gained several extensions in HTML:

• translate, hidden, tabIndex, accessKey, draggable, dropzone, contentEditable, contextMenu, spellcheck and style reflect content attributes.

• dataset is a convenience feature for handling the data-* attributes, which are exposed as camel-cased properties; for instance, elm.dataset.fooBar = 'test' sets the data-foo-bar content attribute on elm.

• WHATWG HTML has itemScope, itemType, itemId, itemRef, itemProp, properties and itemValue for microdata.

• click(), focus() and blur() allow scripts to simulate clicks and moving focus.

• accessKeyLabel gives the shortcut key that the user agent has assigned for the element, which the Web developer can influence with the accesskey attribute.

• isContentEditable returns true if the element is editable.

• forceSpellCheck() causes the user agent to check spelling of an element.

• commandType, commandLabel, commandIcon, commandHidden, commandDisabled and commandChecked is part of the command API.

• All event handler IDL attributes.

Some members were previously defined on HTMLElement but been moved to the Element interface in the DOM standard: [DOM]

• id reflects the id content attribute.

• className reflects the class content attribute.

• classList is a convenient accessor for className. The object it returns exposes methods (contains(), add(), remove(), and toggle()) for manipulating the element's classes.

• getElementsByClassName() returns a list of elements with the specified classes.

5.5 Extensions to Other Interfaces

Some interfaces in DOM Level 2 HTML have been extended.

• HTMLOptionsCollection now has a legacy caller, setter creator, and the members add(), remove() and selectedIndex

• HTMLLinkElement and HTMLStyleElement now implement the LinkStyle interface from CSSOM. [CSSOM]

• HTMLFormElement now has a named getter and an indexed getter.

• HTMLSelectElement now has a getter, item() and namedItem() methods, a setter creator, selectedOptions and labels IDL attributes, and members for the form constrain validation API: willValidate, validity, validationMessage, checkValidity() and setCustomValidity().

• HTMLOptionElement now has a constructor Option.

• HTMLInputElement now has the members files, height, indeterminate, list, valueAsDate, valueAsNumber, width, stepUp(), stepDown(), the form constraint validation API members, labels, and members for the text field selection API: selectionStart, selectionEnd, selectionDirection, setSelectionRange() and setRangeText().

• HTMLTextAreaElement now has the members textLength, the form constraint validation API members, labels and the text field selection API members.

• HTMLButtonElement now has the form constraint validation API members and labels.

• HTMLLabelElement now has the member control.

• HTMLFieldSetElement now has the members type, elements and the form constraint validation API members.

• HTMLAnchorElement now has the members relList, text, and implements the URLUtils interface which has the members href, origin, protocol, username, password, host, hostname, port, pathname, search, query and hash. HTMLLinkElement and HTMLAreaElement also have the relList IDL attribute. HTMLAreaElement also implements the URLUtils interface.

• HTMLImageElement now has a constructor Image, and the members naturalWidth, naturalHeight and complete.

• HTMLObjectElement now has the members contentWindow, the form constraint validation API members and a legacy caller.

• HTMLMapElement now has the member images.

• HTMLTableElement now has the members createTBody() and, in WHATWG HTML and W3C HTML5.1, stopSorting().

• In WHATWG HTML and W3C HTML5.1, HTMLTableHeaderCellElement now has the member sort().

• HTMLIFrameElement now has the member contentWindow.

In addition, most new content attributes also have corresponding IDL attributes on the elements' interfaces, e.g. the sizes IDL attribute on HTMLLinkElement which reflects the sizes content attribute.

5.6 Obsolete APIs

Some APIs are now either removed altogether, or marked as obsolete.

All IDL attributes that reflect a content attribute that is itself obsolete, are now also obsolete; for instance, the bgColor IDL attribute on HTMLBodyElement which reflects the obsolete bgcolor content attribute is now obsolete.

The following interfaces are marked obsolete since the elements are obsolete: HTMLAppletElement, HTMLFrameSetElement, HTMLFrameElement, HTMLDirectoryElement and HTMLFontElement.

The HTMLIsIndexElement interface is removed altogether since the HTML parser expands an isindex tag into other elements. The HTMLBaseFontElement interface is also removed since the element has no effect.

The following members of the HTMLDocument interface (which have now moved to Document) are now obsolete: anchors and applets.

6 HTML Changelogs

The changelogs in this section indicate what has been changed in WHATWG HTML, W3C HTML5 and W3C HTML5.1 between somewhat arbitrary dates, often close to publications of the W3C HTML5 or W3C HTML5.1 drafts. Rationale for changes can be found in the public-html@w3.org and whatwg@whatwg.org mailing list archives, and the WHATWG Weekly series of blog posts. More fundamental rationale is being collected on the WHATWG Rationale wiki page. Many editorial and minor technical changes are not included in these changelogs. Implementors are strongly encouraged to follow the development of the main specification on a frequent basis so they become aware of all changes that affect them early on.

The changes in the changelogs are in rough reverse chronological order.

6.1 Changes from 14 September 2012 to 6 May 2013

• The canvas 2d context has a new method isPointInStroke(). (WHATWG HTML and W3C HTML5.1.)

• The DataTransferItemList interface (part of drag and drop API) now has a remove() method instead of a deleter. (WHATWG HTML and W3C HTML5.1.)

• The registerProtocolHandler() API now supports bitcoin: and geo: schemes. (bitcoin: is WHATWG HTML only.)

• The alert(), confirm() and prompt() methods now have all arguments optional. (WHATWG HTML and W3C HTML5.1.)

• The fieldset element can now match the :invalid pseudo-class. (WHATWG HTML and W3C HTML5.1.)

• The HTMLBaseFontElement interface has been removed. (WHATWG HTML and W3C HTML5.1.)

• The specification has integrated with the URL standard which effectively added the origin, username, password and query IDL attributes to the a and area elements and the location object. (WHATWG HTML and W3C HTML5.1.)

• The hgroup element has been dropped. (W3C HTML5 and W3C HTML5.1.)

• The HTML parser now better supports innerHTML on non-HTML elements. (WHATWG HTML and W3C HTML5.1.)

• Various things that were present in WHATWG HTML but missing in W3C HTML5.1 were "un-forked": The download attribute on a and area, the application cache prefer-online feature, the text range API on input and textarea, the cssElementMap IDL attribute on Document, various bits for microdata. (W3C HTML5.1 only.)

• The drag and drop API now has a dragexit event. (WHATWG HTML and W3C HTML5.1.)

• The form element now recieves an invalid event when submission fails due to form validation (in addition to the individual controls). (WHATWG HTML and W3C HTML5.1.)

• The navigator object now has a product IDL attribute that always returns "Gecko" (for compatibility). (WHATWG HTML and W3C HTML5.1.)

• The time element's datetime IDL attribute got renamed to dateTime. (WHATWG HTML and W3C HTML5.1.)

• The pushState() and replaceState() methods can now be invoked with null as the third argument.

• A new main element has been added.

• The stepUp() and stepDown() methods on the input element have been tweaked. (WHATWG HTML and W3C HTML5.1.)

• The img element now supports progress events. (WHATWG HTML and W3C HTML5.1.)

• A new fillRule IDL attribute has been added to the canvas 2d context. (WHATWG HTML only.)

• The style IDL attribute on HTML elements is now settable. (WHATWG HTML and W3C HTML5.1.)

• The media attribute has been dropped from the a and area elements. (WHATWG HTML and W3C HTML5.1.)

• Heading elements now support automatic sizing in hgroup if they follow an h1 element. (WHATWG HTML only.)

• The navigator object now has a language IDL attribute. (WHATWG HTML and W3C HTML5.1.)

• The menu API has been revamped. The command element was dropped. An new menuitem element was added. The menu element's type attribute now uses the value "popup" instead of "context". The button element has a new menu attribute and the type attribute supports a new value "menu". (WHATWG HTML and W3C HTML5.1.)

• The table element now supports sorting columns. The table element has a new sortable attribute and a stopSorting() method. The th element has a new sorted attribute and a sort() method. (WHATWG HTML and W3C HTML5.1.)

• The autocomplete attribute on form controls now supports the cc-type type. (WHATWG HTML and W3C HTML5.1.)

• A new currentScript IDL attribute on document was added. (WHATWG HTML and W3C HTML5.1.)

• The link and script elements now support the crossorigin attribute. (WHATWG HTML and W3C HTML5.1.)

• The canvas element now supports indirect and proxied rendering contexts, to support drawing from a worker. The CanvasProxy, ImageBitmap interfaces are introduced, the canvas element has new setContext() and transferControlToProxy() methods, and a new createImageBitmap() method on window was introduced. (WHATWG HTML and W3C HTML5.1.)

• The canvas 2d context has a new direction IDL attribute. (WHATWG HTML only.)

• The screen object has a new canvasResolution IDL attribute. (WHATWG HTML only.)

• A new PortCollection() constructor was added to support sending messages to many ports while allowing them to be garbage collected. (WHATWG HTML only.)

• The getItem() method on Storage can now return null. (WHATWG HTML only.)

• The sandbox attribute on iframe supports a new value "allow-pointer-lock". (WHATWG HTML and W3C HTML5.1.)

• The HTML parser now invokes mutation observers. (WHATWG HTML and W3C HTML5.1.)

• The canvas element has a new supportsContext() method. (WHATWG HTML and W3C HTML5.1.)

• The abbr attribute on the th element is now conforming.

• A new forceSpellCheck() method on HTML elements was added. (WHATWG HTML and W3C HTML5.1.)

• The EventSource API now reconnects for DNS errors and TCP-level connection failures. (WHATWG HTML only.)

• A new fastSeek() method was added to media elements. (WHATWG HTML and W3C HTML5.1.)

• The http+aes: and https+aes: schemes were removed due to lack of interest. (WHATWG HTML only.)

• Navigations with rel=noreferrer now does not clone the sessionStorage.

• The error event for Worker objects now has a column IDL attribute. (WHATWG HTML only.)

• The autofocus attribute on form controls in dialog elements now has an effect when the showModal() method is invoked.

6.2 Changes from 29 March 2012 to 14 September 2012

• The content model for ruby was changed with regards to nested ruby elements.

• Self-closing SVG script tags in the HTML syntax now execute.

• The placeholder section for the find() API has been dropped.

• An encoding declaration is now required in the HTML syntax even if only ASCII characters are used.

• Some bug fixes in the Drag and Drop API.

• The inBandMetadataTrackDispatchType IDL attribute was added to TextTrack.

• The TextTrackCue() constructor now has fewer arguments.

• The accept attribute now supports file extensions as well as MIME types.

• The initialTime IDL attribute on media elements has been dropped.

• The startOffsetTime IDL attribute on media elements has been renamed to startDate.

Further changes to WHATWG HTML that do not affect W3C HTML5:

• Several changes and bug fixes in the Text Track API.

• addElement() was dropped from the Drag and Drop API.

• Media queries are now proxied for iframe elements with the seamless attribute.

• The :enabled and :disabled pseudo-classes now apply to input elements in the Hidden state.

• The ssh, sip and magnet schemes are now in the registerProtocolHandler() whitelist.

• table elements now have 'box-sizing:border-box' by default.

• Bug fixes in the "potentially CORS-enabled fetch" algorithm.

• The document outline algorithm now ignores elements with the hidden attribute.

• Markup generators that are unable to provide required alt text can now use a specific attribute on img that makes validators ignore the missing alt error.

• Workers and shared workers now support data: URLs.

• The inputmode attribute has been added to input and textarea.

• The autocomplete attribute has been extended to support prefilling specific things.

• WebSocket supports sending ArrayBufferView as well as ArrayBuffer.

• The border attribute on table is non-conforming again.

• The canvas ImageData methods now assume 96dpi, and a set of "HD" methods have been introduced.

• The shared worker connect event now also exposes the source port in the source IDL attribute.

• Lone surrogates are converted to U+FFFD instead of throwing in WebSocket send().

• The setRangeText() method has been added to input and textarea.

• The srcset attribute has been added to img.

• Application cache now has an prefer-online mode.

• Dialogs are now supported with the dialog element, the inert global attribute and the dialog method on form.

• The resetTransform() method, currentTransform IDL attribute, several IDL attributes for font metrics, resetClip() method, imageSmoothingEnabled IDL attribute, addHitRegion() method, removeHitRegion() method, support for dashed lines, have been added to the canvas 2d context.

6.3 Changes from 25 May 2011 to 29 March 2012

• Support for mutation observers was added.

• The TextTrackCue members alignment, linePosition, textPosition and direction were renamed to align, line, position and vertical, respectively.

• The command element now has a command attribute.

• Drag and drop content is now suggested to be filtered by user agents to prevent XSS attacks.

• The translate global attribute was added.

• The showModalDialog(), alert(), confirm() and prompt() methods are now allowed to do nothing during pagehide, beforeunload and unload events.

• The script element now supports beforescriptexecute and afterscriptexecute events.

• window.onerror now supports a fourth argument for column position.

• The window.opener IDL attribute can now return null in some cases.

• The clearTimeout() and clearInterval() methods were made synonymous.

• The CSS @global at-rule was introduced, for use together with style elements with the scoped attribute.

• The embed and object elements now have a legacy caller.

• The handling of window.onerror's return value was changed to match reality.

• The setTimeout() API is now allowed to be throttled in background tabs.

• The :valid and :invalid pseudo-classes now apply to form elements.

• The toBlob() method on canvas now honors the origin-clean flag.

• The activeElement IDL attribute now points to the relevant browsing context container (e.g. iframe) when a child document has focus.

• The atob() method now ignores whitespace.

• The dropzone attribute was changed to use "string:" and "file:" instead of "s:" and "f:".

• The HTML parser was fixed to correctly handle a case involving foreign lands and foster parenting.

• The date-and-time microsyntaxes now allows a single space instead of a "T".

• Application cache no longer checks the MIME type of the cache manifest.

• The cueAsSource IDL attribute on TextTrackCue got renamed to text.

• The window.onerror API is now invoked with dummy arguments for cross-origin scripts.

• The textarea element's value and textLength IDL attributes have their newlines normalized to LF.

• The q element now has language-specific quotes rendered by default.

• The data element was introduced.

• The time element was redesigned to make it match how people wanted to use it. Its pubdate attribute was dropped.

• The legacy caller on form was removed.

• The location.resolveURL() method was removed.

• The track element now sniffs instead of obeying the MIME type.

• The load() method on documents created by createDocument() is now defined on the XMLDocument interface.

• Members of HTMLDocument moved to Document and window.HTMLDocument now just returns window.Document.

• The MutableTextTrack and TextTrack interfaces were merged and TextTrackCue was made more mutable.

• The selectedOption IDL attribute on input was dropped.

• Attribute values in Selectors are now case sensitive for all attributes.

• The readyState IDL attribute moved from TextTrack to HTMLTrackElement.

• The text/html-sandboxed MIME type was dropped.

• Floating point numbers are now allowed to begin with a "." character.

• Navigating to an audio or video resource is now supported.

• Table cells now allow flow content but does not allow header, footer, sectioning content or heading content descendants.

• Adding a track to a media element now fires an addtrack event on the relevant track list objects.

• Setting currentTime on media elements before the media has loaded now defers the seek instead of throwing.

• Plugins are no longer disabled in sandboxed iframes if they honor the sandbox attribute.

• Some tweaks to history navigation and related events.

• Media elements and MediaControllers now get paused when they end.

• Events now support constructors and some init*Event() methods were removed.

• Media elements now fire a suspend event when the resource is loaded.

• Form submission now normalizes newlines to CRLF.

• Some tweaks around bidi and the br element.

• Large parts of the Editing section moved to HTML Editing APIs.

• UndoManager and related features moved to UndoManager and DOM Transaction.

• isProtocolHandlerRegistered(), isContentHandlerRegistered(), unregisterProtocolHandler() and unregisterContentHandler() were added.

• registerContentHandler() now has a blacklist of MIME types.

• registerProtocolHandler() now has a whitelist of protocols, but also supports any protocol that starts with "web+".

• Fragment identifiers for text/html resources now don't need to point to an element with a matching ID.

• audio elements are now allowed to have zero source children.

• There are now some restrictions on the use of bidi formatting characters.

• The maxlength and size attributes are allowed (but give warnings in validators) on input elements with type=number.

• The link relation "shortcut icon" is now allowed.

• Heading elements are now allowed to have the heading and tab roles.

• Things that use EventTarget now inherit from it instead of using "implements".

• The setInterval() API now clamps to 4ms instead of 10ms.

• The select element and its options collection now have a setter.

• rel=help on links now show a help cursor by default.

• Calls to window.print() before the document is loaded defers the print until it is loaded.

• Application cache gained an abort() method.

• HTMLCollection, DOMTokenList, getElementsByClassName(), createHTMLDocument(), HTML-specific overrides to some DOM Core features (like createElement()), some definitions, the id IDL attribute and ID handling moved to DOM4.

• Fragment identifiers can now survive redirects.

• The pushState() and replaceState() methods now change the history entry to GET.

• The command API now has its properties prefixed so they are now commandLabel, commandIcon, commandHidden, commandDisabled and commandChecked.

• The structured clone algorithm now supports sparse arrays.

• window.postMessage now supports transferring some objects instead of cloning them, and supports transferring ArrayBuffer.

• Application cache was made stricter in its MIME type checking.

• The placeholder attribute is now allowed on input elements with type=number.

• MediaController gained an onended event listener.

• The HTML parser changed its handling of U+0000 characters in some places.

• The object element gained a new attribute typemustmatch, to make it safer for Web developers to embed untrusted resources where they expect a certain content type.

• The form attribute was removed from meter and progress.

• The HTML parser was made more forward compatible in its handling of ruby.

• Some MIME types (e.g. text/plain) that are guaranteed to never be supported as scripting types for script were specified, so Web developers can safely use them for custom data blocks.

• about:blank documents created from window.open() now get a load event.

• window.status was specified to exist but do nothing.

• Drag and drop DataTransferItems was renamed to DataTransferItemList.

• Application cache now supports 'no-store' and HTTPS.

• The structured clone algorithm now supports getters.

• The crossorigin attribute has been added to img, video and audio to use CORS.

• The external IDL attribute has been added on window and has the members AddSearchProvider() and IsSearchProviderInstalled().

Further changes to WHATWG HTML that do not affect W3C HTML5:

• The 2d context now supports ellipses with the arc() and arcTo() methods and the new ellipse() method.

• The 2d context now supports Path objects. SVG path data can be added to a Path.

• The http+aes: and https+aes: URL schemes were added to allow sensitive resources to be held on untrusted servers.

• When the itemprop attribute is used on an element where microdata gets its value from an attribute (like href on a elements), that attribute is now required.

• PeerConnection was moved to WebRTC.

• WebVTT was moved to its own specification.

• WebSockets no longer receive messages in the CLOSING state.

• The Atom conversion algorithm was dropped.

• The itemtype attribute now allows multiple types.

• CanvasPixelArray was dropped in favor of Uint8ClampedArray.

• The microdata to RDF conversion algorithm was dropped.

• The link element is no longer allowed to have both rel and itemprop.

• WebSocket API disallows opening an insecure connection if the document uses a secure connection.

• The "storage mutex" is made optional.

• Web Storage no longer supports structured data.

• The a element got a new download attribute. This attribute is not included in W3C HTML5.

• An experimental specification for the window.find() method was added.

• The 2d context fillText() and strokeText() methods now do not collapse whitespace.

• Microdata now handles infinite loops.

• Web Worker location now stringifies.

• Script errors in a Web Worker can now be detected in a parent worker or the document with the onerror handler.

• EventSource now supports CORS.

• EventSource was made stricter in its MIME type checking.

• Web Workers gained the atob() and btoa() methods.

• Web Workers gained the ononline and onoffline event handlers.

• WebSockets API has the error event again.

• WebSockets API now exposes the selected extensions.

• Various tweaks to the UDP PeerConnection API.

• WebSocket close code and reason are now supported in the API.

• Binary data is now supported in WebSockets.

• Redirects in WebSockets are now blocked for security reasons.

6.4 Changes from 5 April 2011 to 25 May 2011

• Support for the javascript: scheme in img, object, CSS, etc, has been dropped.

• The toBlob() method has been added to canvas.

• The drawFocusRing() method on the canvas 2d context has been split into two methods, drawSystemFocusRing() and drawCustomFocusRing().

• The values attribute on PropertyNodeList has been replaced with a getValues() method.

• The select event has been specified.

• The selectDirection IDL attribute has been added to input and textarea.

• The :enabled and :disabled pseudo-classes now match fieldset, and the :indeterminate pseudo-class can now match progress.

• The getKind() method has been added to TrackList.

• The MediaController API and the mediagroup attribute have been added to synchronize playback of media elements.

• Some ARIA defaults have changed, and it is now invalid to specify ARIA attributes that match the defaults.

• The getName() method on TrackList was renamed to getLabel().

• The border attribute on table is now conforming.

• The u element is now conforming.

• The summary attribute on table is now non-conforming.

• The audio attribute on video was changed to a boolean muted attribute.

• The Content-Language meta pragma is now non-conforming.

6.5 Changes from 13 January 2011 to 5 April 2011

• The pushState and replaceState features have been changed based on implementation feedback in Firefox, and history.state has been introduced.

• The tracks IDL attribute on media elements has been renamed to textTracks.

• Event handler content attributes now support JavaScript strict mode.

• The forminput and formchange events, and the dispatchFormInput() and dispatchFormChange() methods have been dropped.

• The rel keywords archives, up, last, index, first and related synonyms have been dropped.

• Removing a media element from the DOM and inserting it again in the same script now doesn't pause the media element.

• The video element's letterboxing rules are now specified in terms of CSS 'object-fit'.

• Cross-origin fonts now don't leak information about the font when drawn on a canvas.

• The character encoding declaration is now allowed to be within the first 1024 bytes instead of the first 512 bytes.

• The onerror event handler on window is now invoked for compile-time script errors as well as runtime errors.

• Script-inserted script elements now have async default to true, which can be set to false to make the scripts execute in insertion order.

• The atob() and btoa() methods have been specified.

• The suggested file extension for application cache manifest files has been changed from .manifest to .appcache.

• The action and formaction attributes are no longer allowed to have the empty string as value.

6.6 Changes from 19 October 2010 to 13 January 2011

• Drag and drop model was refined.

• A new global dropzone attribute was added.

• A new bdi element was added to aid with user-generated content that may have bidi implications.

• The dir attribute gained a new "auto" value.

• A dirname attribute was added to input elements. When specified the directionality as specified by the user will be submitted to the server as well.

• A new track element and associated TextTrack API were added for video text tracks.

• The type attribute on the ol element is now allowed.

The getSelection() API moved to a separate DOM Range draft. Similarly UndoManager has been removed from the W3C copy of HTML5 for now as it is not ready yet.

6.7 Changes from 24 June 2010 to 19 October 2010

• Numerous changes to the HTML parsing algorithm based on implementation feedback.

• The hidden attribute now works for table-related elements.

• The canvas getContext() method is now defined to be able to handle multiple contexts better.

• The media elements' startTime IDL attribute was renamed to initialTime and startOffsetTime was added.

• The prefetch link relationship can now be used on a elements.

• The datetime attribute of ins and del no longer requires a time to be specified.

• Using PUT and DELETE as HTTP methods for the form element is no longer supported.

• The s element is no longer deprecated.

• The video element has a new audio attribute.

Per usual, lots of other minor fixes have been made as well.

6.8 Changes from 4 March 2010 to 24 June 2010

• The ping attribute has been removed from the W3C version of HTML5.

• The title element is optional for iframe srcdoc documents and other scenarios where a title is already available. As is the case with email.

• keywords is now a standard metadata name for the meta element.

• The allow-top-navigation value has been added for the sandbox attribute on the iframe element. It allows the embedded content to navigate its parent when specified.

• The wbr element has been added.

• The alternate keyword for the rel attribute of the link element can now be used to point to feeds again, even if the feed is not an alternative for the document.

• The HTML to Atom mapping has been removed from the W3C version of HTML5.

In addition lots of minor changes, clarifications, and fixes have been made to the document.

6.9 Changes from 25 August 2009 to 4 March 2010

• The dialog element has been removed. A section with advice on how to mark up conversations has effectively replaced it.

• document.head has been introduced to provide convenient access to the head element from script.

• The link type feed has been removed. alternate with specific media types is to be used instead.

• createHTMLDocument() has been introduced as API to allow easy creation of HTML documents.

• Both the meter and progress elements no longer have "magic" processing of their contents because it could not be made to work internationally.

• The meter and progress elements, as well as the output element, can now be labeled using the label element.

• A new media type, text/html-sandboxed, was introduced to allow hosting of potentially hostile content without it causing harm.

• A srcdoc attribute for the iframe element was introduced to allow embedding of potentially hostile content inline. It is expected to be used together with the sandbox and seamless attributes.

• The figure element now uses a new element figcaption rather than legend because people want to use HTML long before it reaches W3C Recommendation.

• The details element now uses a new element summary for exactly the same reason.

• The autobuffer attribute on media elements was renamed to preload.

A whole lot of other smaller issues have also been resolved. The above list summarizes what is thought to be of primary interest to Web developers.

In addition to all of the above, Microdata, the 2D context API for canvas, and Web Messaging (postMessage() API) have been split into their own drafts at the W3C (the WHATWG still publishes a version of HTML that includes them):

• HTML Microdata

• HTML Canvas 2D Context

• HTML5 Web Messaging

Specific microdata vocabularies are gone altogether in the W3C draft of HTML5 and are not published as a separate draft. The WHATWG draft of HTML still includes them.

6.10 Changes from 23 April 2009 to 25 August 2009

• When the time element is empty user agents have to render the time in a locale-specific manner.

• The load event is dispatched at Window, but now has Document as its target.

• pushState() now affects the Referer (sic) header.

• onundo and onredo are now on Window.

• Media elements now have a startTime member that indicates where the current resource starts.

• header has been renamed to hgroup and a new header element has been introduced.

• createImageData() now also takes ImageData objects.

• createPattern() can now take a video element as argument too.

• The footer element is no longer allowed in header and header is not allowed in address or footer.

• A new control has been introduced: <input type="tel">

• The Command API now works for all elements.

• accesskey is now properly defined.

• section and article now take a cite attribute.

• A new feature called Microdata has been introduced which allows people to embed custom data structures in their HTML documents.

• Using the Microdata model three predefined vocabularies have also been included: vCard, vEvent, and a model for licensing.

• Drag and drop has been updated to work with the Microdata model.

• The last of the parsing quirks has been defined.

• textLength has been added as member of the textarea element.

• The rp element now takes phrasing content rather than a single character.

• location.reload() is now defined.

• The hashchange event now fires asynchronously.

• Rules for compatibility with XPath 1.0 and XSLT 1.0 have been added.

• The spellcheck IDL attribute now maps to a DOMString.

• hasFeature() support has been reduced to a minimum.

• The Audio() constructor sets the autobuffer attribute.

• The td element is no longer allowed in thead.

• The input element and DataTransfer object now have a files IDL attribute.

• The datagrid and bb have been removed due to their design not being agreed upon.

• The cue range API has been removed from the media elements.

• Support for WAI-ARIA has been integrated.

On top of this list quite a few minor clarifications, typos, issues specific to implementors, and other small problems have been resolved.

In addition, the following parts of HTML have been taken out and will likely be further developed at the IETF:

• Definition of URLs.

• Definition of Content-Type sniffing.

6.11 Changes from 12 February 2009 to 23 April 2009

• A new global attribute called spellcheck has been added.

• Defined that JavaScript this in the global object returns a WindowProxy object rather than the Window object.

• The value IDL attribute for input elements in the File Upload state is now defined.

• Definition of designMode was changed to be more in line with legacy implementations.

• The drawImage() method of the 2D drawing API can now take a video element as well.

• The way media elements load resources has been changed.

• document.domain is now IPv6-compatible.

• The video element gained an autobuffer boolean attribute that serves as a hint.

• You are now allowed to specify the meta element with a charset attribute in XML documents if the value of that attribute matches the encoding of the document. (Note that it does not specify the value, it is just a talisman.)

• The bufferingRate and bufferingThrottled members of media elements have been removed.

• The media element resource selection algorithm is now asynchronous.

• The postMessage() API now takes an array of MessagePort objects rather than just one.

• The second argument of the add() method on the select element and the options member of the select element is now optional.

• The action, enctype, method, novalidate, and target attributes on input and button elements have been renamed to formaction, formenctype, formmethod, formnovalidate, and formtarget.

• A "storage mutex" concept has been added to deal with separate pages trying to change a storage object (document.cookie and localStorage) at the same time. The Navigator gained a getStorageUpdates() method to allow it to be explicitly released.

• A syntax for SVG similar to MathML is now defined so that SVG can be included in text/html resources.

• The placeholder attribute has been added to the textarea element.

• Added a keygen element for key pair generation.

• The datagrid element was revised to make the API more asynchronous and allow for unloaded parts of the grid.

In addition, several parts of HTML have been taken out and will be further developed by the Web Applications Working Group as standalone specifications:

• WebSocket API

• WebSocket protocol

• Server-Sent Events

• Web Storage (localStorage and sessionStorage)

• Web SQL Database

6.12 Changes from 10 June 2008 to 12 February 2009

• The data member of ImageData objects has been changed from an array to a CanvasPixelArray object.

• Shadows are now required from implementations of the canvas element and its API.

• Security model for canvas is clarified.

• Various changes to the processing model of canvas have been made in response to implementation and Web developer feedback. E.g. clarifying what happens when NaN and Infinity are passed and fixing the definitions of arc() and arcTo().

• innerHTML in XML was slightly changed to improve round-tripping.

• The toDataURL() method on the canvas element now supports setting a quality level when the media type argument is image/jpeg.

• The poster attribute of the video element now affects its intrinsic dimensions.

• The behavior of the type attribute of the link element has been clarified.

• Sniffing is now allowed for link when the expected type is an image.

• A section on URLs is introduced dealing with how URL values are to be interpreted and what exactly Web developers are required to do. Every feature of the specification that uses URLs has been reworded to take the new URL section into account.

• It is now explicit that the href attribute of the base element does not depend on xml:base.

• It is now defined what the behavior should be when the base URL changes.

• URL decomposition IDL attributes are now more aligned with Internet Explorer.

• The xmlns attribute with the value http://www.w3.org/1999/xhtml is now allowed on all HTML elements.

• data-* attributes and custom attributes on the embed element now have to match the XML Name production and cannot contain a colon.

• WebSocket API is introduced for bidirectional communication with a server.

• The default value of volume on media elements is now 1.0 rather than 0.5.

• event-source was renamed to eventsource because no other HTML element uses a hyphen.

• A message channel API has been introduced augmenting postMessage().

• A new element named bb has been added. It represents a user agent command that the user can invoke.

• The addCueRange() method on media elements has been modified to take an identifier which is exposed in the callbacks.

• It is now defined how to mutate a DOM into an infoset.

• The parent attribute of the Window object is now defined.

• The embed element is defined to do extension sniffing for compatibility with servers that deliver Flash as text/plain. (This is marked as an issue in the specification to figure out if there is a better way to make this work.)

• The embed can now be used without its src attribute.

• getElementsByClassName() is defined to be ASCII case-insensitive in quirks mode for consistency with CSS.

• In HTML documents localName no longer returns the node name in uppercase.

• data-* attributes are defined to be always lowercase.

• The opener attribute of the Window object is not to be present when the page was opened from a link with target="_blank" and rel="noreferrer".

• The top attribute of the Window object is now defined.

• The a element now allows nested flow content, but not nested interactive content.

• It is now defined what the header element means to document summaries and table of contents.

• What it means to fetch a resource is now defined.

• Patterns are now required for the canvas element.

• The autosubmit attribute has been removed from the menu element.

• Support for outerHTML and insertAdjacentHTML() has been added.

• xml:lang is now allowed in HTML when lang is also specified and they have the same value. In XML lang is allowed if xml:lang is also specified and they have the same value.

• The frameElement attribute of the Window object is now defined.

• An event loop and task queue is now defined detailing script execution and events. All features have been updated to be defined in terms of this mechanism.

• If the alt attribute is omitted a title attribute, an enclosing figure element with a legend element descendant, or an enclosing section with an associated heading must be present.

• The irrelevant attribute has been renamed to hidden.

• The definitionURL attribute of MathML is now properly supported. Previously it would have ended up being all lowercase during parsing.

• User agents must treat US-ASCII as Windows-1252 for compatibility reasons.

• An alternative syntax for the DOCTYPE is allowed for compatibility with some XML tools.

• Data templates have been removed (consisted of the datatemplate, rule and nest elements).

• The media elements now support just a single loop attribute.

• The load() method on media elements has been redefined as asynchronous. It also tries out files in turn now rather than just looking at the type attribute of the source element.

• A new member called canPlayType() has been added to the media elements.

• The totalBytes and bufferedBytes attributes have been removed from the media elements.

• The Location object gained a resolveURL() method.

• The q element has changed again. Punctuation is to be provided by the user agent again.

• Various changes were made to the HTML parser algorithm to be more in line with the behavior Web sites require.

• The unload and beforeunload events are now defined.

• The IDL blocks in the specification have been revamped to be in line with the upcoming Web IDL specification.

• Table headers can now have headers. User agents are required to support a headers attribute pointing to a td or th element, but Web developers are required to only let them point to th elements.

• Interested parties can now register new http-equiv values.

• When the meta element has a charset attribute it must occur within the first 512 bytes.

• The StorageEvent object now has a storageArea attribute.

• It is now defined how HTML is to be used within the SVG foreignObject element.

• The notification API has been dropped.

• How [[Get]] works for the HTMLDocument and Window objects is now defined.

• The Window object gained the locationbar, menubar, personalbar, scrollbars, statusbar and toolbar attributes giving information about the user interface.

• The application cache section has been significantly revised and updated.

• document.domain now relies on the Public Suffix List. [PSL]

• A non-normative rendering section has been added that describes user agent rendering rules for both obsolete and conforming elements.

• A normative section has been added that defines when certain selectors as defined in the Selectors and the CSS3 Basic User Interface Module match HTML elements. [SELECTORS] [CSSUI]

Web Forms 2.0, previously a standalone specification, has been fully integrated into HTML since last publication. The following changes were made to the forms chapter:

• Support for XML submission has been removed.

• Support for form filling has been removed.

• Support for filling of the select and datalist elements through the data attribute has been removed.

• Support for associating a field with multiple forms has been removed. A field can still be associated with a form it is not nested in through the form attribute.

• The dispatchChangeInput() and dispatchFormChange() methods have been removed from the select, input, textarea, and button elements.

• Repetition templates have been removed.

• The inputmode attribute has been removed.

• The input element in the File Upload state no longer supports the min and max attributes.

• The allow attribute on input elements in the File Upload state is no longer authoritative.

• The pattern and accept attributes for textarea have been removed.

• RFC 3106 is no longer explicitly supported.

• The submit() method now just submits, it no longer ensures the form controls are valid.

• The input element in the Range state now defaults to the middle, rather than the minimum value.

• The size attribute on the input element is now conforming (rather than deprecated).

• object elements now partake in form submission.

• The type attribute of the input element gained the values color and search.

• The input element gained a multiple attribute which allows for either multiple e-mails or multiple files to be uploaded depending on the value of the type attribute.

• The input, button and form elements now have a novalidate attribute to indicate that the form fields should not be required to have valid values upon submission.

• When the label element contains an input it may still have a for attribute as long as it points to the input element it contains.

• The input element now has an indeterminate IDL attribute.

• The input element gained a placeholder attribute.

6.13 Changes from 22 January 2008 to 10 June 2008

• Implementation and authoring details around the ping attribute have changed.

• <meta http-equiv=content-type> is now a conforming way to set the character encoding.

• API for the canvas element has been cleaned up. Text support has been added.

• globalStorage is now restricted to the same-origin policy and renamed to localStorage. Related event dispatching has been clarified.

• postMessage() API changed. Only the origin of the message is exposed, no longer the URL. It also requires a second argument that indicates the origin of the target document.

• Drag and drop API has got clarification. The dataTransfer object now has a types attribute indicating the type of data being transferred.

• The m element is now called mark.

• Server-sent events has changed and gotten clarification. It uses a new format so that older implementations are not broken.

• The figure element no longer requires a caption.

• The ol element has a new reversed attribute.

• Character encoding detection has changed in response to feedback.

• Various changes have been made to the HTML parser section in response to implementation feedback.

• Various changes to the editing section have been made, including adding queryCommandEnabled() and related methods.

• The headers attribute has been added for td elements.

• The table element has a new createTBody() method.

• MathML support has been added to the HTML parser section. (SVG support is still awaiting input from the SVG WG.)

• Web developer-defined attributes have been added. Web developers can add attributes to elements in the form of data-name and can access these through the DOM using dataset[name] on the element in question.

• The q element has changed to require punctuation inside rather than having the browser render it.

• The target attribute can now have the value _blank.

• The showModalDialog API has been added.

• The document.domain API has been defined.

• The source element now has a new pixelratio attribute useful for videos that have some kind encoding error.

• bufferedBytes, totalBytes and bufferingThrottled IDL attributes have been added to the video element.

• Media begin event has been renamed to loadstart for consistency with the Progress Events specification.

• charset attribute has been added to script.

• The iframe element has gained the sandbox and seamless attributes which provide sandboxing functionality.

• The ruby, rt and rp elements have been added to support ruby annotation.

• A showNotification() method has been added to show notification messages to the user.

• Support for beforeprint and afterprint events has been added.

Acknowledgments

The editors would like to thank Ben Millard, Bruce Lawson, Cameron McCormack, Charles McCathieNevile, Dan Connolly, David Håsäther, Dennis German, Frank Ellermann, Frank Palinkas, Futomi Hatano, Gordon P. Hemsley, Henri Sivonen, James Graham, Jens Meiert, Jeremy Keith, Jukka K. Korpela, Jürgen Jeka, Krijn Hoetmer, Leif Halvard Silli, Maciej Stachowiak, Mallory van Achterberg, Marcos Caceres, Mark Pilgrim, Martijn Wargers, Martin Leese, Martyn Haigh, Masataka Yakura, Michael Smith, Mike Taylor, Ms2ger, Olivier Gendrin, Øistein E. Andersen, Philip Jägenstedt, Philip Taylor, Randy Peterman, Steve Faulkner, Toby Inkster, Xaxio Brandish, and Yngve Spjeld Landro for their contributions to this document as well as to all the people who have contributed to HTML over the years for improving the Web!

References