HTML 5 differences from HTML 4

W3C Working Draft 23 April 2009

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Anne van Kesteren (Opera Software ASA) <annevk@opera.com>


HTML 5 defines the fifth major revision of the core language of the World Wide Web, HTML. "HTML 5 differences from HTML 4" describes the differences between HTML 4 and HTML 5 and provides some of the rationale for the changes. This document may not provide accurate information as the HTML 5 specification is still actively in development. When in doubt, always check the HTML 5 specification itself. [HTML5]

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 23 April 2009 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 HTML 5 specification. The appropriate forum for comments is public-html-comments@w3.org, a mailing list with a public archive.

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 Introduction

HTML has been in continuous evolution since it was introduced to the Internet in the early 1990's. 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 continue to diverge.

HTML 4 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 XHTML 1, which defines an XML serialization for HTML 4, and DOM Level 2 HTML, which defines JavaScript APIs for both HTML and XHTML. HTML 5 will replace these documents. [DOM2HTML] [HTML4] [XHTML1]

The HTML 5 draft reflects an effort, started in 2004, to study contemporary HTML implementations and deployed content. The draft:

  1. Defines a single language called HTML 5 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

HTML 5 is still a draft. The contents of HTML 5, as well as the contents of this document which depend on HTML 5, are still being discussed on the HTML Working Group and WHATWG mailing lists. The open issues include (this list is not exhaustive):

1.2 Backwards Compatible

HTML 5 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 specification clearly separates requirements for authors and user agents. 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 HTML 5 has separate conformance requirements for authors and user agents there is no longer a need for marking features "deprecated".

1.3 Development Model

The HTML 5 specification will not be considered finished before there are at least two complete implementations of the specification. This is a different approach than previous versions of HTML had. The goal is to ensure that the specification is implementable and usable by designers and developers once it is finished.

1.4 Impact on Web Architecture

The following areas / features defined in HTML 5 are believed to impact the Web architecture:

2 Syntax

HTML 5 defines an HTML syntax that is compatible with HTML 4 and XHTML 1 documents published on the Web, but is not compatible with the more esoteric SGML features of HTML 4, such as the NET syntax (i.e. <em/content/). Documents using the HTML syntax must be served with the text/html media type.

HTML 5 also defines detailed parsing rules (including "error handling") for this syntax which are largely compatible with popular 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 HTML 5 is XML. This syntax is compatible with XHTML 1 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 HTML 5. Note that XML documents must have 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 of HTML 5 authors have three means of setting the character encoding:

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


The HTML syntax of HTML 5 requires a DOCTYPE to be specified to ensure that the browser renders the page in standards mode. The DOCTYPE has no other purpose and is therefore optional for XML. Documents with an XML media type are always handled in standards mode. [DOCTYPE]

The DOCTYPE declaration is <!DOCTYPE html> and is case-insensitive in the HTML syntax. DOCTYPEs from earlier versions of HTML were longer because the HTML language was SGML-based and therefore required a reference to a DTD. With HTML 5 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>.

2.3 MathML and SVG

The HTML syntax of HTML 5 allows for MathML and SVG elements to be used inside a document. E.g. 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>

More complex combinations are also possible. E.g. with the SVG foreignObject element you could nest MathML, HTML, or both inside an SVG fragment that is itself inside HTML.

2.4 Miscellaneous

There are a few other syntax changes worthy of mentioning:

3 Language

This section is split up in several subsections to more clearly illustrate the various differences there are between HTML 4 and HTML 5.

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

HTML 5 has introduced several new attributes to various elements that were already part of HTML 4:

Several attributes from HTML 4 now apply to all elements. These are called global attributes: class, dir, id, lang, style, tabindex and title.

There are also several new global attributes:

HTML 5 also makes all event handler attributes from HTML 4 that take the form onevent-name global attributes and adds several new event handler attributes for new events it defines, such as the onmessage attribute which can be used together with the new eventsource element and the cross-document messaging API.

3.3 Changed Elements

These elements have slightly modified meanings in HTML 5 to better reflect how they are used on the Web or to make them more useful:

3.4 Absent 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 HTML 5 define how. E.g. the obsolete isindex element is handled by the parser section.

The following elements are not in HTML 5 because their effect is purely presentational and their function is better handled by CSS:

The following elements are not in HTML 5 because their usage affected usability and accessibility for the end user in a negative way:

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 is only conforming in the HTML syntax. It is not included in the XML syntax as its usage relies on an HTML parser.

3.5 Absent Attributes

Some attributes from HTML 4 are no longer allowed in HTML 5. If they need to have any impact on user agents for compatibility reasons it is defined how they should work in those scenarios.

In addition, HTML 5 has none of the presentational attributes that were in HTML 4 as their functions are better handled by CSS:

4 APIs

HTML 5 introduces a number of APIs that help in creating Web applications. These can be used together with the new elements introduced for applications:

4.1 Extensions to HTMLDocument

HTML 5 has extended the HTMLDocument interface from DOM Level 2 HTML in a number of ways. The interface is now implemented on all objects implementing the Document interface so it stays meaningful in a compound document context. It also has several noteworthy new members:

4.2 Extensions to HTMLElement

The HTMLElement interface has also gained several extensions in HTML 5:

5 HTML 5 Changelogs

The changelogs in this section indicate what has been changed between publications of the HTML 5 drafts. Rationale for changes can be found in the public-html@w3.org and whatwg@whatwg.org mailing list archives and to some extent in the This Week in HTML 5 series of blog posts. Many editorial and minor technical changes are not included in these changelogs. I.e. 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 to ease editing this document.

5.1 Changes since 12 February 2009

In addition, several parts of HTML 5 have been taken out and will be further developed by the Web Applications Working Group as standalone specifications:

5.2 Changes from 10 June 2008 to 12 February 2009

Web Forms 2.0, previously a standalone specification, has been fully integrated into HTML 5 since last publication. The following changes were made to the forms chapter:

5.3 Changes from 22 January 2008 to 10 June 2008


The editor would like to thank Ben Millard, Cameron McCormack, Charles McCathieNevile, Dan Connolly, David Håsäther, Frank Ellermann, Henri Sivonen, James Graham, Jens Meiert, Jürgen Jeka, Maciej Stachowiak, Mark Pilgrim, Martijn Wargers, Martyn Haigh, Masataka Yakura, Michael Smith, Olivier Gendrin, Øistein E. Andersen, Philip Taylor and Simon Pieters for their contributions to this document as well as to all the people who have contributed to HTML 5 over the years for improving the Web!


CSS3 Basic User Interface Module, T. Çelik, editor. W3C, May 2004.
Activating Browser Modes with Doctype, H. Sivonen, January 2008.
Document Object Model (DOM) Level 2 HTML Specification, J. Stenback, P. Le Hégaret, A. Le Hors, editors. W3C, January 2003.
HTML 4.01 Specification, D. Raggett, A. Le Hors, I. Jacobs, editors. W3C, December 1999.
HTML 5, I. Hickson, D. Hyatt, editors. W3C, February 2009.
HTML 5 (editor's draft), I. Hickson, editor. WHATWG, 2009.
HTML 5 (editors' draft), I. Hickson, D. Hyatt, editors. W3C, 2009.
Public Suffix List, Mozilla Foundation, 2007.
Selectors, D. Glazman, T. Çelik, I. Hickson, editors. W3C, December 2005.
XHTML™ 1.1 - Module-based XHTML (Second Edition), S. McCarron, M. Ishikawa, editors. W3C, February 2007.
Extensible Markup Language (XML) 1.0 (Fifth Edition), T. Bray, J. Paoli, C. Sperberg-McQueen, E. Maler, F. Yergeau, editors. W3C, November 2008.
Namespaces in XML 1.0 (Second Edition), T. Bray, D. Hollander, A. Layman, R. Tobin, editors. W3C, August 2006.