public function URL($path = '', $current_url = null)
    {
        $url = new URL($this->url);
        $path = ltrim($path, '/');
        $url->set('path', $url->path . $path);

        if ($current_url instanceof URL)
        {
            if ($url->host === $current_url->host && $url->scheme === $current_url->scheme && $url->port === $current_url->port)
            {
                $url->host = null;
                $url->scheme = null;
            }
        }
        return $url;
    }