private function setCurrentUserAgent()
    {
        $ua = mb_strtolower(trim($this->current_word));
        if ($this->previous_directive !== self::DIRECTIVE_USERAGENT) {
            $this->current_UserAgent = [];
        }
        $this->current_UserAgent[] = $ua;

        // create empty array if not there yet
        if (empty($this->rules[$ua])) {
            $this->rules[$ua] = [];
        }
    }