[oever]

DTD does not know about namespaces and checks against "prefix:local-name".

E.g. the xhtml dtd will not accept this:

  <h:html xmlns:h="http://www.w3.org/1999/xhtml"/>

If you want to change prefixes, use XML Schema or Relax NG.

[Ygg2]

DTD is the devil spawn. Devil here being massive security vulnerabilities.

[lyxsus]

I would say use XML Schema at least. DTD looks alien to XML anyway.