public function filter($value)
    {
        if (!self::$_unicodeEnabled) {
            // POSIX named classes are not supported, use alternative 0-9 match
            $pattern = '/[^0-9]/';
        } else {
            if(extension_loaded('mbstring')){
                $pattern = '/[^[:digit:]]/';
            }else{
                $pattern = '/[\p{^N}]/';
            }
        }

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