XHTML 1.0 was the first major change to the HTML since 1997, and
a very important step on the way to create a standard that will
provide richer web pages on a wider range of user agents
(browsers), like desktop PCs, mobile (wireless) devices, and
XHTML is an XML application with clean
migration path from HTML 4.01. W3C's first step was to
reformulate HTML 4.01 into XML, resulting in XHTML 1.0. XHTML
1.0 relies on HTML 4.01 for the meanings of HTML tags.
The next step include modularization of XHTML into smaller
element collections, to make it easier to combine XHTML with
other markup languages like vector graphics and multimedia.
Modularization of XHTML also gives reduced development cost,
improved cooperation with other applications (like databases),
easier communication with different user agents (browsers), and
cleaner integration between HTML and different XML standards.