One of the most impressive features of XML (eXtensible Markup Language) is how little you need to know to get started. This appendix gives you some of the key pieces of information. For more information, see one of the many books being released on the topic or the references at the end of Chapter 3, "User Accounts".
Thanks to the ubiquity of XML's older and stodgier cousin, HTML, almost everyone is familiar with the notion of a markup language. Like HTML, XML consists of plain text interspersed with little bits of special descriptive or instructive text. HTML has a rigid definition for which bits of markup text, called tags, are allowed, while XML allows you to make up your own.
XML provides a range of expression far beyond that of HTML. We see an example of this expression in Chapter 3, "User Accounts", but here's another simple example that should be easy to read even without any prior XML experience:
<machine> <name> quidditch </name> <department> Software Sorcery </department> <room> 129A </room> <owner> Harry Potter </owner> <ipaddress> 192.168.1.13 </ipaddress> </machine>
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