static public function rUrl($url)
    {
        $module = null;
        if (strpos($url, 'http') !== 0 && ($pos = strpos($url, ':')) !== false) {    // 1. "x:a/b" module or xUrl
            $module = trim(substr($url, 0, $pos), '/');
            $url   = trim(substr($url, $pos + 1), '/');
        }
        
        if (strpos($url, 'http') === 0) {
            $url = str_replace(static::url($module . ':'), '', $url);
        }
        
        return trim($url, '/');
    }