HTML and CSS Reference
Chapter 15. XML
HTML is a maverick. It only loosely follows the rules of formal electronic
document-markup design and implementation. The language was born
out of the need to assemble text, graphics, and other digital content and
send them over the global Internet. In the early days of the Web's boom,
the demand for better browsers and document serversdriven by hordes
of new users with insatiable appetites for more and cooler web pagesleft
little time for worrying about things like standards and practices.
Of course, without guiding standards, HTML would eventually have de-
volved into Babel. That almost happened, during the browser wars in the
mid- to late 1990s. Chaos is not an acceptable foundation for an industry
whose value is measured in the trillions of dollars. Although the stand-
ards people at the World Wide Web Consortium (W3C) managed to rein
in the maverick HTML with standard version 4, it is still too wild for the
royal herd of markup languages.
The HTML 4.01 standard is defined using the Standard Generalized
Markup Language (SGML). While more than adequate for formalizing
HTML, SGML is far too complex to use as a general tool for extending and
enhancing HTML. Instead, the W3C has devised a standard known as the
Extensible Markup Language, or XML. Based on the simpler features of
SGML, XML is kinder, gentler, and more flexible, well suited to guiding
the birth and orderly development of new markup languages. With XML,
HTML is being reborn as XHTML.
In this chapter, we cover the basics of XML, including how to read it,
how to create simple XML Document Type Definitions (DTDs), and the
ways you might use XML to enhance your use of the Internet. In the next
chapter, we explore the depths of XHTML.
You don't have to understand everything there is to know about XML to
write XHTML. We think it's helpful, but if you want to cut to the chase,
feel free to skip to the next chapter. Before you do, however, you may
want to take a look at some of the uses of XML covered at the end of this
chapter, starting with section 15.8 .