code: def validateDtd(self, doc, dtd):
          
          if doc is None: doc__o = None
          else: doc__o = doc._o
          if dtd is None: dtd__o = None
          else: dtd__o = dtd._o
          ret = libxml2mod.xmlValidateDtd(self._o, doc__o, dtd__o)
          return ret
docs: Try to validate the document against the dtd instance
            Basically it does check all the definitions in the DtD.
            Note the the internal subset (if present) is de-coupled
            (i.e. not used), which could give problems if ID or IDREF
             is present.