Changes from HTML4

Global overview

HTML5 is different from HTML4 in a way that it addresses both document and application semantics making it more suitable for the web applications created today. HTML5 also reflects implementations better where they differ from HTML4 to ensure the language is implementable and compatible with the web. Inspired by the forward compatible error handling in CSS HTML5 defines detailed processing models where necessary to ensure that implementations become interoperable and that the language stays extensible in the future.

Syntax

• HTML5 specifies its own syntax rules authors have to follow. These syntax rules are compatible with the XHTML syntax rules althoug this does not imply that parsing such a document with an HTML parser will give the same result as parsing it with an XML parser.

• HTML5 defines its own parsing rules (including "error correction") for text/html resources and no longer assumes SGML features are supported.

New elements

Document Structure

• article
• aside
• dialog
• figure
• footer
• header
• nav
• section

Data

• audio
• embed
• m
• meter
• source
• time
• video

Applications

• canvas
• command
• datagrid
• details
• datalist (Web Forms 2)
• event-source
• output (Web Forms 2)
• progress

Changed elements

These elements have a new meaning in HTML5 which is incompatible with HTML4. The new meaning better reflects the way they are used on the web or gives them a purpose so people can start using them.

• b
• hr
• i
• menu
• small
• strong

Dropped elements

That these elements are dropped means that authors are no longer allowed to use them. User agents will still have to support them and HTML5 will probably get a rendering section in due course that says exactly how. (isindex for instance is already supported by the parser.)

• acronym (use abbr instead)
• applet (use object instead)
• basefont
• big
• center
• dir
• frame
• frameset
• isindex
• noframes
• noscript (only dropped in XHTML5)
• s
• strike
• tt
• u