DTDs really are the thing that should never have been in XML. Namespaces in XML make them pretty useless, given they only have a concept of QNames and not names

DTDs really are the thing that should never have been in XML. Namespaces in XML make them pretty useless, given they only have a concept of QNames and not namespace URL & local name tuples, and they don't compose in any sensible way. They are such a large part of the complexity of the XML it's just sad.