private function isPrefixedKey($key)
    {
        if (strlen($key) > 1) {
            if (substr($key, 0, 1) == '_') {
                try {
                    intval(substr($key, 1, strlen($key) - 1));

                    return true;
                } catch (\Exception $e) {
                    return false;
                }
            }
        }
    }