Hmm, this line of thought may be perpetuating what I see as one of
the shortcomings of DTDs, namely that the DTD has to describe the
whole document, i.e. a class of languages. What about partial
validation/constraints? I think it's important that child-of-DTD
support compond documents & partial validation. So in the terms above,
maybe these things define sets of elements and attributes, rather
than whole documents. -Tim