| Running Scared |

If you've been playing with XML for a while, you probably already know that XML documents come in two flavours: well-formed and valid.

A well-formed document is one which meets the specifications laid down in the XML recommendation - that it, it follows the rules for element and attribute names, contains all essential declarations, and has
properly-nested elements.

A valid document is one which, in addition to being well-formed, adheres to the rules laid out in a DTD or XML Schema. By imposing some structure on an XML document, a DTD makes it possible for documents to conform to some standard rules, and for applications to avoid nasty surprises in the form of incompatible or invalid data.

If you're serious about developing your XML skill set, you're going to bump your head up against DTDs sooner or later - and the arcane commands and symbols you find will make you want to weep and beg for Mommy. Unless, of course, you're armed with your own secret weapon...

This article.

Over the course of the next few pages, I'm going to find out just what makes a DTD tick, with examples, explanations and illustrations that will demystify this simple yet surprisingly-scary piece of the XML puzzle. Strap yourself in, and prepare to meet the beast!

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