While HTML, prior to HTML5, was defined as an application of Standard Generalized Markup Language (SGML), a flexible markup language framework, XHTML is an application of XML, a more restrictive subset of SGML.
XHTML documents are well-formed and may therefore be parsed using standard XML parsers, unlike HTML, which requires a lenient HTML-specific parser.
while at the same time updating the HTML specifications to address issues raised in the past few years." Ian Hickson, editor of the HTML5 specification criticising the improper use of XHTML in 2002, December 1998 saw the publication of a W3C Working Draft entitled Reformulating HTML in XML.
This introduced Voyager, the codename for a new markup language based on HTML 4, but adhering to the stricter syntax rules of XML.
First, there are some differences in syntax: The similarities between HTML 4.01 and XHTML 1.0 led many web sites and content management systems to adopt the initial W3C XHTML 1.0 Recommendation.
To aid authors in the transition, the W3C provided guidance on how to publish XHTML 1.0 documents in an HTML-compatible manner, and serve them to browsers that were not designed for XHTML.
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.
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.
By February 1999 the name of the specification had changed to XHTML 1.0: The Extensible Hyper Text Markup Language, and in January 2000 it was officially adopted as a W3C Recommendation.