protected function assertValidId($id)
    {
        if (defined('PHP_WINDOWS_VERSION_BUILD')) {
            $bad = preg_match('/[\x00-\x1F\x7F]\<\>\:\"\|\?\*]/', $id);
        } else {
            $bad = preg_match('/\x00/', $id);
        }
        if ($bad) {
            throw new RawFileCacheException('Invalid character found in cache ID', RawFileCacheException::INVALID_CHARACTER);
        }
    }