Load document from xml using bytes offset information.
        XXX: this is not tested under Windows.

def _get_doc_by_raw_offset(self, doc_id):
        """
        Load document from xml using bytes offset information.
        XXX: this is not tested under Windows.
        """
        bounds = self._get_meta()[str(doc_id)].bounds
        return xml_utils.load_chunk(self.filename, bounds)