private function matchMode($modeElement)
    {
        if (!empty($modeElement)) {
            $mode = $modeElement[0];
            if (!$mode) {
                return $this->matchMode;
            }
            if (!self::validMatchMode($mode)) {
                throw new WURFL_WURFLException('Invalid Match Mode: '.$mode);
            }
            $this->matchMode = $mode;
        }
        return $this->matchMode;
    }