HTML and CSS Reference
XHTML and the Development of HTML5
Near the end of the 1990s, the W3C released the fi nal specifi cations for the 4 th ver-
sion of HTML, called HTML 4, and began charting a course for the next version. The
path chosen by the W3C was to reformulate HTML in terms of XML. XML ( Extensible
Markup Language ) is a compact offshoot of SGML and is used to defi ne new markup
languages, known as XML vocabularies . A document based on an XML vocabulary is
forced to obey specifi c rules for content and structure to avoid being rejected as invalid.
By contrast, HTML allows for a wide variety in syntax between one HTML document
and another. Another important aspect of XML is that several XML vocabularies can be
combined within a single document, making it easier to extend XML into different areas
The W3C developed an XML vocabulary that was a stricter version of HTML4, known
as XHTML ( Extensible Hypertext Markup Language ). XHTML was designed to confront
some of the problems associated with the various competing versions of HTML and to
better integrate HTML with other markup languages. Because XHTML was an XML ver-
sion of HTML, most of what Web designers used with HTML could be applied to XHTML
with only a few modifi cations, and many tools and features associated with XML could
be easily applied to XHTML.
By 2002, the W3C had released the specifi cations for XHTML 1.1. This version was
intended to be only a minor upgrade on the way to XHTML 2.0 , which would contain
a set of XML vocabularies moving HTML into the future with robust support for mul-
timedia, social networking, interactive Web forms, and other features needed by Web
designers. One problem was that XHTML 2.0 would not be backward compatible with
earlier versions of HTML and thus older Web sites could not be easily integrated with the
proposed new standard.
Web designers rebelled at this development. In 2004, Ian Hickson, who was work-
ing for Opera Software at the time, proposed a different path. Hickson's proposal would
have allowed for the creation of new Web applications while still maintaining backward
compatibility with HTML 4. He argued that HTML was whatever the browser market
determined it to be, and that trying to enforce a new specifi cation that did not accommo-
date the needs and limitations of the market was a fruitless exercise.
Hickson's proposal was rejected by the W3C and, in response, a new group of Web
designers and browser manufacturers formed the Web Hypertext Application Technology
Working Group (WHATWG) with the mission to develop a rival version to XHTML 2.0,
called HTML5 . For several years, it was unclear which specifi cation would represent the
future of the Web; but by 2006, work on XHTML 2.0 had completely stalled. The W3C
issued a new charter for an HTML Working Group to develop HTML5 as the next HTML
specifi cation. Work on XHTML 2.0 was halted in 2009, leaving HTML5 as the de facto
standard for the next generation of HTML.