php操作xml字符串

$str = '

    Success
    ok
    0
    -8307280112529702907
    1
';
        $xml = new \DOMDocument();
        $xml->loadXML($str);
        $res = $xml->getElementsByTagName( "returnsms");
        $message = $status = '';
        foreach($res as $value ) {
            $message = $value->getElementsByTagName('message')->item(0)->nodeValue;
            $status = $value->getElementsByTagName('returnstatus')->item(0)->nodeValue;
        }
        if ($message == 'Success' && $status == 'ok'){
            return true;
        }else{
            return false;
        }