function xrds($force=null)
    {
        if($force) {
            echo $this->xrdsContent();
            die();
        } elseif($force === false) {
            header('X-XRDS-Location: '. $this->xrdsLocation);
            return;
        }
        
        if (isset($_GET['xrds'])
            || (isset($_SERVER['HTTP_ACCEPT']) &&  strpos($_SERVER['HTTP_ACCEPT'], 'application/xrds+xml') !== false)
        ) {
            header('Content-Type: application/xrds+xml');
            echo $this->xrdsContent();
            die();
        }
        
        header('X-XRDS-Location: ' . $this->xrdsLocation);
    }