HTML and CSS Reference
16.1. Why XHTML?
As we described in the preceding chapter, HTML began as a simple
markup language similar in appearance and usage to other Standard
Generalized Markup Language (SGML)-based markup languages. In its
early years, little effort was put into making HTML perfectly SGML com-
pliant. As a result, odd features and a lax attitude toward enforcing the
rules became standard parts of both HTML and the browsers that pro-
cessed HTML documents.
As the Web grew from an experiment into an industry, the desire for a
standard version of HTML led to the creation of several official versions,
culminating most recently with version 4.01. As HTML has stabilized into
this latest version, browsers have become more alike in their support of
various HTML features. In general, the world of HTML has settled into a
familiar set of constructs and usage rules.
Unfortunately, HTML offers only a limited set of document-creation prim-
itives, is incapable of handling nontraditional content such as chemical
formulae, musical notation, or mathematical expressions, and fails to ad-
equately support alternative display media such as handheld computers
or intelligent cellular phones. We need new ways to deliver information
that can be parsed, processed, displayed, sliced, and diced by the many
different communication technologies that have emerged since the Web
sparked the digital communication revolution a decade ago.
Instead of trying to rein in another herd of maverick, nonstandard
markup languages, the W3C introduced XML as a standard way to create
new markup languages. XML is the framework upon which organiza-
tions can develop their own markup languages to suit the needs of their
users. XML is an updated version of SGML, streamlined and enhanced for
today's dynamic systems. And while the W3C originally intended it as a
tool to create document markup languages, XML is also becoming quite
useful as a standard way to define small languages that different applic-
ations use as data-exchange protocols.
Of course, we don't want to abandon the plethora of documents already
marked up with HTML, or the infrastructure of knowledge, tools, and