Try to validate the document instance  basically it does
          the all the checks described by the XML Rec i.e. validates
          the internal and external subset (if present) and validate
           the document tree.

def validateDocument(self, doc):
        """Try to validate the document instance  basically it does
          the all the checks described by the XML Rec i.e. validates
          the internal and external subset (if present) and validate
           the document tree. """
        if doc is None: doc__o = None
        else: doc__o = doc._o
        ret = libxml2mod.xmlValidateDocument(self._o, doc__o)
        return ret