private function blacklistCheck($input)
    {
        foreach ([
                     'mozilla',
                     'compatible',
                     '(',
                     ')',
                 ] as $string) {
            if (stripos($input, $string) !== false) {
                throw new Exceptions\FormatException('Invalid User-agent format (`' . trim($this->product . '/' . $this->version, '/') . '`). Examples of valid User-agents: `MyCustomBot`, `MyFetcher-news`, `MyCrawler/2.1` and `MyBot-images/1.2`. See also ' . self::RFC_README);
            }
        }
        return true;
    }