def isRef(self, elem, attr):
        """Determine whether an attribute is of type Ref. In case we
          have DTD(s) then this is simple, otherwise we use an
           heuristic: name Ref (upper or lowercase). """
        if elem is None: elem__o = None
        else: elem__o = elem._o
        if attr is None: attr__o = None
        else: attr__o = attr._o
        ret = libxml2mod.xmlIsRef(self._o, elem__o, attr__o)
        return ret