Setup an xmltextReader to parse a preparsed XML document.
           This reuses the existing @reader xmlTextReader.

def NewWalker(self, doc):
        """Setup an xmltextReader to parse a preparsed XML document.
           This reuses the existing @reader xmlTextReader. """
        if doc is None: doc__o = None
        else: doc__o = doc._o
        ret = libxml2mod.xmlReaderNewWalker(self._o, doc__o)
        return ret