HTML 5 differences from HTML 4

Abstract

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 a First Public 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
  • 1.1 Open Issues
  • 1.2 Backwards Compatible
  • 1.3 Development Model
  • 1.4 Impact on Web Architecture
• 2. Syntax
  • 2.1 Character Encoding
  • 2.2 The DOCTYPE
  • 2.3 Miscellaneous
• 3. Language
  • 3.1 New Elements
  • 3.2 New Attributes
  • 3.3 Changed Elements
  • 3.4 Absent Elements
  • 3.5 Absent Attributes
• 4. APIs
  • 4.1 Extensions to HTMLDocument
  • 4.2 Extensions to HTMLElement
• 5. HTML 5 Changelog
• Acknowledgments
• References

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 XHTML1, which defines an XML serialization for HTML 4, and DOM Level 2 HTML, which defines JavaScript APIs for both HTML and XHTML. [ HTML4 ] [ XHTML1 ] [ DOM2HTML ]

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 a "custom" 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. Some of the open issues include (this list is not exhaustive):

• De facto semantic definitions for some formerly presentational elements.
• Details of accessibility and media-independence features, such as the longdesc , alt and summary attributes.
• The repetition model.

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 this is why the specification clearly separates requirements for authors and user agents. This means that authors can not use the isindex or plaintext element, but user agents are required to support them in a way that is compatible with how these elements behaved previously.

Since HTML 5 has separate conformance requirements for authors and user agents there is no longer a need for marking things "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:

• The use of the DOM as a basis for defining the language.
• The concept of browsing contexts.
• The distinction between user agent requirements and authoring requirements.
• The use of imperative definitions rather than abstract definitions with the requirement of black-box equivalence in implementations.
• The new content model concepts (replacing HTML 4's block and inline concepts).
• The focus on accessibility as a built-in concept for new features (such as the irrelevant attribute, the progress element, et cetera) instead of an add-on (like the alt attribute).
• The focus on defining the semantics in detail (e.g. the outline algorithm, replacing the vague semantics in HTML 4).
• The server-sent events feature (the event-source element).
• The datagrid element.
• The menu and command elements.
• The origin concept.
• Offline Web application caches.
• The definition of the browsing context "navigation" algorithm and the related session history traversal algorithms.
• The content-type sniffing and character encoding sniffing.
• The very explicit definition of a parser.
• The two structured storage features.
• The contentEditable feature and the UndoManager feature.
• The Drag and Drop and Copy and Paste architecture.
• The cross-document messaging feature (the postMessage API).
• The new sandboxing features for iframe .

2. Syntax

The HTML 5 language has a "custom" HTML syntax that is compatible with HTML 4 and XHTML1 documents published on the Web, but is not compatible with the more esoteric SGML features of HTML 4, such as <em/content/ . Documents using this "custom" syntax must be served with the text/html MIME type.

HTML 5 also defines detailed parsing rules (including "error handling") for this syntax which are largely compatible with popular implementations. User agents will follow these rules for resources that have the text/html MIME 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 5 is XML. This syntax is compatible with XHTML1 documents and implementations. Documents using this syntax need to be served with an XML MIME 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 MIME type such as application/xhtml+xml or application/xml .

<?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 of HTML 5 authors have three means of setting the character encoding:

• At the transport level. By using the HTTP Content-Type header for instance.
• 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 as the first element child of the head element. <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">

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 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 MIME type are always handled in standards mode. [ DOCTYPE ]

The DOCTYPE declaration is <!DOCTYPE html> and is case-insensitive in the HTML syntax. DOCTYPE s 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 Miscellaneous

There are a few other syntax changes worthy of mentioning:

• HTML now has native support for IRIs. In HTML 4 this was only handled as error handling.
• The lang attribute takes the empty string in addition to a valid language identifier, just like xml:lang does in XML.

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:

• section represents a generic document or application section. It can be used together with h1 - h6 to indicate the document structure.

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

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

• header represents the header of a section.

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

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

• dialog can be used to mark up a conversation like this:

  <dialog>
   <dt> Costello
   <dd> Look, you gotta first baseman?
   <dt> Abbott
   <dd> Certainly.
   <dt> Costello
   <dd> Who's playing first?
   <dt> Abbott
   <dd> That's right.
   <dt> Costello
   <dd> When you pay off the first baseman every month, who gets the money?
   <dt> Abbott
   <dd> Every dollar of it. 
  </dialog>
  
  

• figure can be used to associate a caption together with some embedded content, such as a graphic or video:

  <figure>
   <video src=ogg>…</video>
   <legend>Example</legend>
  </figure>
  
  

Then there are several other new elements:

• audio and video for multimedia content. Both provide an API so application authors 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.

• embed is used for plugin content.

• mark represents a run of marked text.

• meter represents a measurement, such as disk usage.

• time represents a date and/or time.

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

• command represents a command the user can invoke.

• datagrid represents an interactive representation of a tree list or tabular data.

• details represents additional information or controls which the user can obtain on demand.

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

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

• The datatemplate , rule and nest elements provide a templating mechanism for HTML.

• event-source is used to "catch" server sent events.

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

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

• The ruby , rt and rb elements allow for marking up ruby annotations.

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

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

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:

• The a and area elements now have a media attribute for consistency with the link element. It is purely advisory.

• The a and area elements have a new attribute called ping that specifies a space separated list of URIs which have to be pinged when the hyperlink is followed. Currently user tracking is mostly done through redirects. This attribute allows the user agent to inform users which URIs are going to be pinged as well as giving privacy-conscious users a way to turn it off.

• The area element, for consistency, now has the hreflang and rel attributes.

• The base element can now have a target attribute as well mainly for consistency with the a element and because it was already widely supported. Also, the target attribute for the a and area elements is no longer deprecated, as it is useful in Web applications, for example in conjunction with iframe .

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

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

• 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 as the user can turn it off if he does not like it, for instance.

• The new form attribute for input , output , select , textarea , button and fieldset elements allows for controls to be associated with more than a single form.

• The input , button and form elements have a new replace attribute which affects what will be done with the document after a form has been submitted.

• The form and select elements (as well as the datalist element) have a data attribute that allows for automatically prefilling of form controls, in case of form , or the form control, in case of select and datalist , with data from the server.

• The new required attribute applies to input (except when the type attribute is hidden , image or some button type such as submit ) and textarea . It indicates that the user has to fill in a value in order to submit the form.

• The input and textarea elements have a new attribute called inputmode which gives a hint to the user interface as to what kind of input is expected.

• You can now disable an entire fieldset by using the disabled attribute on it. This was not possible before.

• The input element has several new attributes to specify constraints: autocomplete , min , max , pattern and step . As mentioned before it also has a new list attribute which can be used together with the datalist and select element.

• input and button also have a new template attribute which can be used for repetition templates.

• The menu element has three new attributes: type , label and autosubmit . 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.

• 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) to indicate the size of the referenced icon.

• The ol element has a new attribute called reversed to indicate that the list order is descending when present.

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

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:

• 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 author.
• The draggable attribute can be used together with the new drag & drop API.
• The irrelevant attribute indicates that an element is not yet, or is no longer, relevant.
• The ref , registrationmark and template global attributes complement the data template feature.
• The data- * collection of author defined attributes. Authors can define any attribute they want as long as they prefix it with data- to avoid clashes with future versions of HTML. The only requirement on these attributes is that they are not used for user agent extensions.

The following are the attributes for the repetition model. These are global attributes and as such may be used on all HTML elements, or on any element in any other namespace, with the attributes being in the http://www.w3.org/1999/xhtml namespace.:

• repeat
• repeat-start
• repeat-min
• repeat-max

HTML 5 also makes all event handler attributes from HTML 4 that take the form on event-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 event-source 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:

• The a element without an href attribute now represents a "placeholder link".

• The address element is now scoped by the new concept of sectioning.

• The b element now represents a span of text to be stylistically offset from the normal prose without conveying any extra importance, such as key words in a document abstract, product names in a review, or other spans of text whose typical typographic presentation is emboldened.

• 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, such as a taxonomic designation, a technical term, an idiomatic phrase from another language, a thought, a ship name, or some other prose whose typical typographic presentation is italicized. Usage varies widely by language.

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

• The menu element is redefined to be useful for actual menus.

• The small element now represents small print (for side comments and legal print).

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

• Quotation marks for the q element are now to be provided by the author rather than the user agent.

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 HTML 5 will get a rendering section in due course that says exactly how. (The isindex element for instance is already supported by the parser.)

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

• basefont
• big
• center
• font
• s
• strike
• tt
• u

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

• frame
• frameset
• noframes

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

• acronym is not included because it has created lots of confusion. Authors 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 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.

• accesskey attribute on a , area , button , input , label , legend and textarea .
• 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 map , img , object , form , iframe , a (use id instead).
• scheme attribute on meta .
• archive , classid , codebase , codetype , declare and standby attributes on object .
• valuetype and type attributes on param .
• language attribute on script .
• summary attribute on table .
• axis and abbr attributes on td and th .
• scope attribute on td .
• headers attribute on th .

In addition, HTML 5 has none of the presentational attributes that were in HTML 4 as they 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 table , img and 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 , input and select .
• type attribute on li , ol 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. 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:

• 2D drawing API which can be used with the new canvas element.
• API for playing of video and audio which can be used with the new video and audio elements.
• Persistent storage. Both key / value and a SQL database are supported.
• An API that enables offline Web applications.
• An API that allows a Web application to register itself for certain protocols or MIME types.
• Editing API in combination with a new global contenteditable attribute.
• Drag & drop API in combination with a draggable attribute.
• Network API.
• API that exposes the history and allows pages to add to it to prevent breaking the back button. (This API has the necessary security restrictions in place.)
• Cross-document messaging.
• Server-sent events in combination with the new event-source element.

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:

• getElementsByClassName() to select elements by their class name. The way this method is defined it will allow it to work for any content with class attributes and a Document object such as SVG and MathML.

• innerHTML as an easy way to parse and serialize an HTML or XML document. This attribute was previously only available on HTMLElement in Web browsers and not part of any standard.

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

• getSelection() which returns an object that represents the current selection(s).

• designMode and execCommand() which are mostly used for editing of documents.

4.2 Extensions to HTMLElement

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

• getElementsByClassName() which is basically a scoped version of the one found on HTMLDocument .

• innerHTML as found in Web browsers today. It is also defined to work in XML context (when it is used in an XML document).

• classList is a convenient accessor for className . The object it returns exposes methods, such as has() , add() , remove() and toggle() for manipulating the element's classes. The a , area and link elements have a similar attribute called relList that provides the same functionality for the rel attribute.

5. HTML 5 Changelog

Below is a rough list of changes that have been made to the HTML 5 specification since the initial publication of the HTML 5 Working Draft. This changelog only indicates what has been changed. For more detailed discussion please use the public-html@w3.org and whatwg@whatwg.org mailing list archives. Changes that affect this document have been incorperated throughout.

• 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 URI. 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.)
• Author defined attributes have been added. Authors 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 punctation 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 DOM attributes hav val