HTML5 differences from HTML4

W3C Working Draft 25 October 2012

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Anne van Kesteren (Opera Software ASA) <annevk@annevk.nl>
Simon Pieters (Opera Software ASA) <simonp@opera.com>


HTML is the core language of the World Wide Web. The W3C publishes HTML5, which is the fifth major revision of HTML. The WHATWG publishes HTML, which is a rough superset of HTML5. "HTML5 differences from HTML4" describes the differences of these documents from HTML4, and calls out cases where HTML is different from HTML5. This document may not provide accurate information as the specifications are still actively in development. When in doubt, always check the specifications themselves. [HTML5] [HTML]

Status of this Document

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

This is the 25 October 2012 W3C Working Draft produced by the HTML Working Group, part of the HTML Activity. The Working Group intends to publish this document as a Working Group Note to accompany the HTML5 specification. The appropriate forum for comments is W3C Bugzilla. (public-html-comments@w3.org, a mailing list with a public archive, is no longer used for tracking comments.)

Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

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

Table of Contents

  1. 1 Introduction
    1. 1.1 Open Issues
    2. 1.2 Backwards Compatible
    3. 1.3 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 HTML5 Changelogs
    1. 6.1 Changes since 29 March 2012
    2. 6.2 Changes from 25 May 2011 to 29 March 2012
    3. 6.3 Changes from 5 April 2011 to 25 May 2011
    4. 6.4 Changes from 13 January 2011 to 5 April 2011
    5. 6.5 Changes from 19 October 2010 to 13 January 2011
    6. 6.6 Changes from 24 June 2010 to 19 October 2010
    7. 6.7 Changes from 4 March 2010 to 24 June 2010
    8. 6.8 Changes from 25 August 2009 to 4 March 2010
    9. 6.9 Changes from 23 April 2009 to 25 August 2009
    10. 6.10 Changes from 12 February 2009 to 23 April 2009
    11. 6.11 Changes from 10 June 2008 to 12 February 2009
    12. 6.12 Changes from 22 January 2008 to 10 June 2008
  7. Acknowledgments
  8. References

1 Introduction

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 author 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 a critical mass of deployed 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. HTML5 will replace these documents. [DOM2HTML] [HTML4] [XHTML1]

The HTML5 draft reflects an effort, started in 2004, to study contemporary HTML implementations and deployed content. The draft:

  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.

1.1 Open Issues

HTML5 is still a draft. The contents of HTML5, as well as the contents of this document which depend on HTML5, are still being discussed on the HTML Working Group and WHATWG mailing lists. The open issues are linked from the HTML5 draft.

1.2 Backwards Compatible

HTML5 is defined in a way that it is backwards compatible with the way user agents handle deployed content. To keep the authoring language relatively simple for authors, several elements and attributes are not included, as outlined in the other sections of this document, such as presentational elements that are better dealt with using CSS.

User agents, however, will always have to support these older elements and attributes and this is why the HTML5 specification clearly separates requirements for authors and user agents. For instance, this means that authors 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 deployed content.

Since HTML5 has separate conformance requirements for authors and user agents there is no longer a need for marking features "deprecated".

1.3 Development Model

The HTML5 specification will not be considered finished before there are at least two complete implementations of the specification. A test suite will be used to measure completeness of the implementations. This approach differs from previous versions of HTML, where the final specification would typically be approved by a committee before being actually implemented. The goal of this change is to ensure that the specification is implementable, and usable by authors once it is finished.

2 Syntax

HTML5 defines an HTML syntax that is 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.

HTML5 also defines detailed parsing rules (including "error handling") for this syntax which are largely compatible with HTML4-era implementations. User agents must 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>
    <meta charset="UTF-8">
    <title>Example document</title>
    <p>Example paragraph</p>

The other syntax that can be used for HTML5 is XML. This syntax is compatible with XHTML1 documents and implementations. Documents using this syntax need to be served with an XML media type 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]

Below is an example document that conforms to the XML syntax of HTML5. Note that XML documents must be served with an XML media type such as application/xhtml+xml or application/xml.

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

2.1 Character Encoding

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

For the XML syntax, authors have to use the rules as set forth in the XML specifications to set the character encoding.

2.2 The Doctype

The HTML syntax of HTML5 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. With HTML5 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 of HTML5 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>
 A green circle:
 <svg> <circle r="50" cx="50" cy="50" fill="green"/> </svg>

2.4 Miscellaneous

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

3 Language

This section is split up in several subsections to more clearly illustrate the various differences there are between HTML4 and HTML5.

3.1 New Elements

The following elements have been introduced for better structure:

Then there are several other new elements:

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

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:

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:

HTML5 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 HTML5 to better reflect how they are used on the Web or to make them more useful:

3.4 Changed Attributes

Several attributes have changed in various ways.

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

3.5 Obsolete Elements

The elements in this section are not to be used by authors. User agents will still have to support them and various sections in HTML5 define how. E.g. the obsolete isindex element is handled by the parser section.

The following elements are not in HTML5 because their effect is purely presentational and their function is better handled by CSS:

The following elements are not in HTML5 because using them damages usability and accessibility:

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

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 HTML5. The specification defines how user agents should process them in legacy documents, but authors must not use them and they will not validate.

HTML5 has advice on what you can use instead.

In addition, HTML5 has none of the presentational attributes that were in HTML4 as their functions are better handled by CSS:

4 Content Model

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 now 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.

HTML5 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.

As broad changes from HTML4, HTML5 no longer has any element that only accepts what HTML4 called "block-level" elements; e.g. the body element now allows flow content. This is thus closer to HTML4 Transitional than HTML4 Strict.

Further changes include:

5 APIs

HTML5 has introduced many new APIs and have extended, changed or obsoleted some existing APIs.

5.1 New APIs

HTML5 introduces a number of APIs that help in creating Web applications. These can be used together with the new elements introduced for applications:

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

5.2 Changed APIs

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

5.3 Extensions to Document

DOM Level 2 HTML had an HTMLDocument interface that inherited from Document and provided HTML-specific members on documents. HTML5 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:

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 HTML5:

5.5 Extensions to Other Interfaces

Some interfaces in DOM Level 2 HTML have been extended.

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.

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

The HTMLIsIndexElement interface is removed altogether since the HTML parser expands an isindex tag into other elements.

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

6 HTML5 Changelogs

The changelogs in this section indicate what has been changed between publications of the HTML5 drafts, as well as changes in WHATWG HTML that do not affect HTML5. 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 chronological order.

6.1 Changes since 29 March 2012

Further changes to WHATWG HTML that do not affect HTML5:

6.2 Changes from 25 May 2011 to 29 March 2012

Further changes to WHATWG HTML that do not affect HTML5:

6.3 Changes from 5 April 2011 to 25 May 2011

6.4 Changes from 13 January 2011 to 5 April 2011

6.5 Changes from 19 October 2010 to 13 January 2011

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.

6.6 Changes from 24 June 2010 to 19 October 2010

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

6.7 Changes from 4 March 2010 to 24 June 2010

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

6.8 Changes from 25 August 2009 to 4 March 2010

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

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 HTML5 that includes them):

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

6.9 Changes from 23 April 2009 to 25 August 2009

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 HTML5 have been taken out and will likely be further developed at the IETF:

6.10 Changes from 12 February 2009 to 23 April 2009

In addition, several parts of HTML5 have been taken out and will be further developed by the Web Applications Working Group as standalone specifications:

6.11 Changes from 10 June 2008 to 12 February 2009

Web Forms 2.0, previously a standalone specification, has been fully integrated into HTML5 since last publication. The following changes were made to the forms chapter:

6.12 Changes from 22 January 2008 to 10 June 2008


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, 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, Toby Inkster, 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!


CSSOM, Glenn Adams, Shane Stephens and Anne van Kesteren. W3C.
CSS Basic User Interface Module, Tantek Çelik. W3C.
Activating Browser Modes with Doctype, Henri Sivonen.
Document Object Model (DOM) Level 2 HTML Specification, Johnny Stenback, Philippe Le Hégaret and Arnaud Le Hors. W3C.
HTML, Ian Hickson. WHATWG.
HTML 4.01 Specification, Dave Raggett, Arnaud Le Hors and Ian Jacobs. W3C.
HTML5, Ian Hickson. W3C.
Public Suffix List. Mozilla Foundation.
Selectors Level 4, Elika J. Etemad. W3C.
XHTML™ 1.1 - Module-based XHTML - Second Edition, Murray Altheim and Shane McCarron.
Extensible Markup Language, Tim Bray, Jean Paoli, C. M. Sperberg-McQueen et al.. W3C.