It shouldn't be hard to do that using XML::ParseDTD — that is, in those cases where it's feasible. After all, if element A may contain element B, and element B may contain element A, there's no way for the generator to know when to stop nesting. I suppose you could just create minimal templates with only the minimum required tags the DTD demands — for the cases I can think of right now, that is always a finite set if not one with only a single member.

Makeshifts last the longest.