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Filename extension .xhtml, .xht,
.xml, .html, .htm
Internet media type application/xhtml+xml
Developed by World Wide Web Consortium
Type of format Markup language
Extended from XML, HTML
Standard(s) 1.0 (Recommendation),

1.1 (Recommendation),
1.1 SE (Working Draft),
5 (Working Draft),

2.0 (Working Draft)

XHTML (Extensible Hypertext Markup Language) is a family of XML markup languages that mirror or extend versions of the widely used Hypertext Markup Language (HTML), the language in which web pages are written.

While HTML (prior to HTML5) was defined as an application of Standard Generalized Markup Language (SGML), a very flexible markup language framework, XHTML is an application of XML, a more restrictive subset of SGML. Because XHTML documents need to be well-formed, they can be parsed using standard XML parsers—unlike HTML, which requires a lenient HTML-specific parser.

XHTML 1.0 became a World Wide Web Consortium (W3C) Recommendation on January 26, 2000. XHTML 1.1 became a W3C Recommendation on May 31, 2001. XHTML5 is undergoing development as of September 2009, as part of the HTML5 specification.



XHTML 1.0 is "a reformulation of the three HTML 4 document types as applications of XML 1.0".[1] The World Wide Web Consortium (W3C) also continues to maintain the HTML 4.01 Recommendation and the specifications for HTML5 and XHTML5 are being actively developed. In the current XHTML 1.0 Recommendation document, as published and revised to August 2002, the W3C commented that, "The XHTML family is the next step in the evolution of the Internet. By migrating to XHTML today, content developers can enter the XML world with all of its attendant benefits, while still remaining confident in their content's backward and future compatibility."[1]

However, in 2004, the Web Hypertext Application Technology Working Group (WHATWG) formed, independently of the W3C, to work on advancing ordinary HTML not based on XHTML. Most major browser vendors were unwilling to implement the features in new W3C XHTML drafts, and felt that they didn't serve the needs of modern web development.[citation needed] The WHATWG eventually began working on a standard that supported both XML and non-XML serializations, HTML 5, in parallel to W3C standards such as XHTML 2. In 2007, the W3C's HTML working group voted to officially recognize HTML 5 and work on it as the next-generated HTML standard.[2] In 2009, the W3C allowed the XHTML 2 Working Group's charter to expire, acknowledging that HTML 5 would be the sole next-generation HTML standard, including both XML and non-XML serializations.[3]


XHTML was developed to make HTML more extensible and increase interoperability with other data formats.[4] HTML 4 was ostensibly an application of Standard Generalized Markup Language (SGML); however the specification for SGML was complex, and neither web browsers nor the HTML 4 Recommendation were fully conformant with it.[5] The XML standard, approved in 1998, provided a simpler data format closer in spirit to HTML 4.[6] By shifting to an XML format, it was hoped HTML would become compatible with common XML tools;[7] servers and proxies would be able to transform content, as necessary, for constrained devices such as mobile phones.[8] By utilizing namespaces, XHTML documents could provide extensibility by including fragments from other XML-based languages such as Scalable Vector Graphics and MathML.[9] Finally, the renewed work would provide an opportunity to divide HTML into reusable components (XHTML Modularization) and clean up untidy parts of the language.[10]

Relationship to HTML

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