This very powerful capability of XML means that in XHTML, where
the tag set is already de?¬? ned for you, there is both a set of custom
tags for your XHTML content and a second document, known as
a DTD (document type de?¬? nition), to explain how to handle those
tags to the device that is interpreting the XHTML. By becoming
XML-compliant, XHTML has been able to transcend the limitations
of HTML and can be expanded over time, and can be shared as realtime
Web services between other data systems. The DOCTYPE tag at
the start of every XHTML Web page makes this critical association
between the markup and the DTD.
XML has been almost universally adopted in business, and the
fact that the same X (for eXtensible) is now in XHTML emphasizes
the unstoppable movement toward the separation of presentation
and content.
The rest of this chapter is dedicated to the latest, completely
reformulated, totally modern, and altogether more ?¬‚ exible version
of HTML.
You can de?¬? ne which type of device
a style sheet relates to using the
link tag??™s media attribute.
If you want more than this rather
simplistic description of XML, check
out the XML tutorial at the SpiderPro
Web site (www.spiderpro.com/bu/
buxmlm001.html).
XHTML: GIVING STRUCTURE TO CONTENT 11
XHTML??”The Rules
Correctly written XHTML markup gives you the best chance that your
pages will display correctly in a broad variety of devices for years to
come.
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