HTML and CSS Reference
In-Depth Information
Chapter 16. XHTML
Despite its name, you don't use the Extensible Markup Language (XML)
to directly create and mark up web documents. Instead, you use XML
to define a new markup language, which you then use to mark up web
documents. This should come as no surprise to anyone who has read the
preceding chapter in this topic. Nor, then, should it surprise you that one
of the first languages defined using XML is an XMLized version of HTML,
the most popular markup language ever. HTML is being disciplined and
cleaned up by XML, to bring it back into line with the larger family of
markup languages. This standard is XHTML 1.0. [*]
[*] Throughout this chapter, we use "XHTML" to mean the XHTML 1.0 standard. There is a nascent
XHTML 1.1 standard that diverges from HTML 4.01 and is more restrictive than XHTML 1.0. We de-
scribe the salient features of XHTML 1.1 in section 16.4 .
Because of HTML's legacy features and oddities, using XML to describe
HTML was not an easy job for the World Wide Web Consortium (W3C). In
fact, certain HTML rules, as we'll discuss later, cannot be expressed with
XML. Nonetheless, if the W3C has its way, XHTML will ultimately replace
the HTML we currently know and love.
So much of XHTML is identical to HTML's current standard, version 4.01,
that you can apply almost everything presented elsewhere in this topic
to both HTML and XHTML. We detail the differences, both good and bad,
in this chapter. To become fluent in XHTML, you'll first need to absorb
the rest of this topic, and then adjust your thinking to embrace what we
present in this chapter.
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