code: def _cross_xAx(self):
          
          crossAx_id = self._element.crossAx.val
          expr = (
              '(../c:catAx | ../c:valAx | ../c:dateAx)/c:axId[@val="%d"]'
              % crossAx_id
          )
          cross_axId = self._element.xpath(expr)[0]
          return cross_axId.getparent()
docs: The axis element in the same group (primary/secondary) that crosses
          this axis.