public function filter($value)
    {
        $whiteSpace = $this->allowWhiteSpace ? '\s' : '';
        if (!self::$_unicodeEnabled) {
            // POSIX named classes are not supported, use alternative a-zA-Z match
            $pattern = '/[^a-zA-Z' . $whiteSpace . ']/';
        } else {

            //$pattern = '/[^\p{L}' . $whiteSpace . ']/u';
            //$pattern = '/[^\p{Ll}\p{Lu}' . $whiteSpace . ']/u';

            if (extension_loaded('mbstring')) {
              $pattern = '/[^[:alpha:]' . $whiteSpace . ']/u';
            }else{
              $pattern = '/[^\p{L}' . $whiteSpace . ']/u';
            }
        }

        return preg_replace($pattern, '', (string) $value);
    }