protected function strip($urlString, $separator = '-')
    {
        if (is_numeric($urlString)) {
            return $urlString;
        }

        $urlString = iconv('UTF-8', 'ASCII//TRANSLIT//IGNORE', $urlString);
        $urlString = preg_replace('#[^\w \-\.]+#i', null, $urlString);
        $urlString = preg_replace('/[ -\.]+/', $separator, $urlString);
        $urlString = trim($urlString, '-.');

        return $urlString;
    }