The axis element in the same group (primary/secondary) that crosses
        this axis.

def _cross_xAx(self):
        """
        The axis element in the same group (primary/secondary) that crosses
        this axis.
        """
        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()