An Eagle’s Eye View of XML

This first chapter introduces you to XML. It explains in

general what XML is and how it is used. It shows you how

the different pieces of the XML equaTIon fit together, and how

an XML document is created and delivered to readers.

What Is XML?

XML stands for Extensible Markup Language (often written as

eXtensibleMarkup Language to jusTIfy the acronym). XML is a

set of rules for defining semanTIc tags that break a document

into parts and idenTIfy the different parts of the document. It

is a meta-markup language that defines a syntax used to define

other domain-specific, semantic, structured markup languages.

XML Is a Meta-Markup Language

The first thing you need to understand about XML is that it

isn’t just another markup language like the Hypertext Markup

Language (HTML) or troff. These languages define a fixed set

of tags that describe a fixed number of elements. If the markup

language you use doesn’t contain the tag you need—you’re

out of luck. You can wait for the next version of the markup

language hoping that it includes the tag you need; but then

you’re really at the mercy of what the vendor chooses to

include.