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Is there something that would cause someone to use DTD rather than XSD or the other way around?
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Yes, many things. One thing is you have to go with what your partners in XML transactions are going to understand. That means using DTDs if it is what they can read/parse/require, and using XSDs if they mandate them.

XSDs are far more expressive but are much newer, so this is a transitional phase.

I personally find them much harder to write but, usually, well-worth it. There are one or two things that are quite nice in DTDs that you miss when you have to express them in XSD syntax but, as the XSD standard progresses, I think these items will be taken care of.

Did you have a particular need or question in mind?

>L<