public static function count($string = false, $selector = false) {

        if ($string) {

            switch ($selector) {
                case 'words':
                    return str_word_count($string);
                default:
                    if (self::substring($selector, 0, 1) === ':') {
                        return substr_count($string, self::substring($selector, 1));
                    }
                    return self::length($string);
            }
        }

        return false;
    }