Document Type Definitions
If the W3C XML Schema Language is a Torx screwdriver, then DTDs are the old reliable flathead screwdriver, not nearly as sexy but a lot more practical and a lot easier to find at the corner store. Contrary to popular belief, schemas do not replace DTDs. DTDs are an extremely well-tested, well-understood, broadly supported, compact syntax for expressing constraints on XML documents. Furthermore, DTDs can do things that none of the other schema languages can accomplish, notably entity definition. Finally, a document can have both a schema and a DTD.
Don't reject DTDs simply because they're not as hip as schemas. Indeed, if your constraints are limited to the element and attribute structure of a document and do not involve ...
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