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).

def isRef(self, doc, 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 doc is None: doc__o = None
        else: doc__o = doc._o
        if attr is None: attr__o = None
        else: attr__o = attr._o
        ret = libxml2mod.xmlIsRef(doc__o, self._o, attr__o)
        return ret