public static function slugify($text, $lowercase = true, $skip_chars = '') {

        // replace non letter or digits by -
        $text = preg_replace('~[^\\pL\d'.$skip_chars.']+~u', '-', $text);
        // trim
        $text = trim($text, '-');
        // transliterate
        $text = iconv('utf-8', 'us-ascii//TRANSLIT', $text);
        // lowercase
        if ($lowercase) $text = strtolower($text);
        // remove unwanted characters
        $text = preg_replace('~[^-\w'.$skip_chars.']+~', '', $text);

        if (empty($text)) {
            return 'n-a';
        }

        return $text;
    }