private function _lock_cData($parser, $cdata) {
        $parserid = (int) $parser;
        if (trim($cdata) <> '') {
            // $this->_error_log(($this->_xmltree[$parserid]) . '='. htmlentities($cdata));
            $this->_lock_ref_cdata .= $cdata;
        } else {
            // do nothing
        }
    }