The XHTML family is a reformulation of HTML 4 in XML. It represents the next step
in the evolution of the Internet. It lets you enter the XML world,
creating content that is both backward and future compatible.
XHTML became an official W3C recommendation on January 26, so when you read this
you are on the cutting edge of it all.
HTML has a fixed set of elements, so it is not easily extended to different needs
HTML was designed with the PC in mind, not taking into account the multitude of
alternative platforms coming to the Web, like TVs, mobile phones and digital tablets.
HTML is defined relatively sloppily, requiring parsers to be quite forgiving
and intelligent in fixing problematic markup on the fly. This intelligence weighs in
heavy on your hard disk with your favorite browser.
So what is there to gain?
Citing the W3C recommendation on XHTML (in rearranged order of my humbly perceived
importance):
"Document developers and user agent designers are constantly discovering new ways to
express their ideas through new markup. In XML, it is relatively easy to introduce new
elements or additional element attributes. The XHTML family is designed to accommodate
these extensions through XHTML modules and techniques for developing new XHTML-conforming
modules (described in the forthcoming XHTML Modularization specification). These modules
will permit the combination of existing and new feature sets when developing content and
when designing new user agents.
Alternate ways of accessing the Internet are constantly being introduced. Some estimates
indicate that by the year 2002, 75% of Internet document viewing will be carried out on
these alternate platforms. The XHTML family is designed with general user agent
interoperability in mind. Through a new user agent and document profiling mechanism,
servers, proxies, and user agents will be able to perform best effort content
transformation. Ultimately, it will be possible to develop XHTML-conforming content that
is usable by any XHTML-conforming user agent.
XHTML documents conform to the XML standard, so they are readily viewed, edited, and
validated with standard XML tools.
XHTML documents can still be written to operate as well or better than they did before in
existing HTML 4-conforming user agents as well as in new, XHTML 1.0 conforming user agents.
XHTML documents can utilize applications (e.g. scripts and applets) that rely upon either
the HTML Document Object Model or the XML Document Object Model [DOM].
As the XHTML family evolves, documents conforming to XHTML 1.0 will be more likely to
interoperate within and among various XHTML environments."
refer to the XHTML namespace http://www.w3.org/1999/xhtml in its root
element.
contain one of the following DOCTYPE declaration prior to the root element:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "DTD/xhtml1-strict.dtd">
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "DTD/xhtml1-transitional.dtd">
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "DTD/xhtml1-frameset.dtd">
Here is an example of a minimal XHTML document:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>My first XHTML page</title>
</head>
<body>
<p>Hello XHTML world!</p>
</body>
</html>
