What is HTML?
HTML is the lingua franca for publishing hypertext on the World Wide Web. It is a non-proprietary format based upon SGML, and can be created and processed by a wide range of tools, from simple plain text editors - you type it in from scratch - to sophisticated WYSIWYG authoring tools. HTML uses tags such as
<h1> and </h1> to structure text into headings, paragraphs, lists, hypertext links etc. Here is a 10-minute guide for newcomers to HTML. W3C's statement of direction for HTML is given on the HTML Activity Statement. See also the page on our work on the next generation of Web forms, and the section on Web history.What is XHTML?
The Extensible HyperText Markup Language (XHTML™) is a family of current and future document types and modules that reproduce, subset, and extend HTML, reformulated in XML rather than SGML. XHTML Family document types are all XML-based, and ultimately are designed to work in conjunction with XML-based user agents. XHTML is the successor of HTML, and a series of specifications has been developed for XHTML. See also: HTML and XHTML Frequently Answered Questions
Recommendations
W3C produces what are known as "Recommendations". These are specifications, developed by W3C working groups, and then reviewed by Members of the Consortium. A W3C Recommendation indicates that consensus has been reached among the Consortium Members that a specification is appropriate for widespread use.
In general, XHTML specifications include implementations of their requirements in various syntaxes (e.g., XML DTD, XML Schema, RelaxNG). These implementations are normative, and are meant to be used either as building blocks for new markup languages (e.g., XHTML Modularization) or as complete markup language implementations (e.g., XHTML 1.1).
While a normative part of the W3C Recommendation in which they are presented, these implementations are also code containing potential errors or omissions. When such errors are discovered, it is sometimes important that they be addressed very quickly to ensure that technologies relying on the implementations work as expected (e.g., validators and content authoring systems). The W3C process allows for the publication and frequent updating of errata, but unfortunately this process does not enable implementations to be quickly updated. As a result, the XHTML 2 Working Group has adopted the following concerning the production and evolution of its implementations:
- All implementations will adhere to the naming convention(s) and evolution rules as defined in XHTML Modularization. These names include both Formal Public Identifiers and System Identifiers. These conventions require that the System Identifier must include a revision number. This revision number is ONLY incremented when a revision is not backward compatible.
- Each applicable Recommendation will include fixed, unchanging versions of those implementations within the formal dated location for the Recommendation (/TR/YYYY/REC-whatever-YYYYmmdd/...).
- The Working Group will also provide a version of that implementation in the working group's space on the W3C server (/MarkUp), uncoupled from a specific dated version of the associated Recommendation. In the beginning this uncoupled version will be *identical* to the version from the associated Recommendation.
- If the Working Group identifies a problem with an implementation, and it is possible to solve the problem in a way that is 100 percent backward compatible, then the version in the group's space will be updated in place and an announcement will be sent to the XHTML 2 public email list.
The XHTML 2 Working Group states that the term "backward compatible" should be used only when:
- The external interface to the module cannot change in any way that would break another module or markup language, either within or outside of the W3C.
- The content model cannot change in any way that would cause a previously valid document to become invalid.
If either of the above constraints would be violated by a change, the working group will either 1) not make the change, or 2) revise the applicable module. In the latter case, the working group will also change the associated identifiers.
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