What do you mean by "the code then creates an HTML form according to that DTD's structure"?

I know a little about XML, and about HTML forms and I haven't a clue as to what you mean.

also, you state that the final output is an XML document, but that the DTD changes as a result of the submission, which leads me to believe that one of us (probably you) is confused, since DTD is not XML.

Could you provide a small example of the input and output you intend?

--Bob Niederman, http://bob-n.com