将具有属性的所有元素设置为某个值

我正试图将属性为"布尔"的给定XML文件的ALL元素的值设置为True，我很难弄清楚如何做到这一点：

    $dom = new DOMDocument('1.0');
    $dom->preserveWhiteSpace = false;
    $dom->formatOutput = true;
    $dom->loadXML($sxe->asXML());
    $xpath = new DOMXPath($dom);
    foreach ($xpath->query('//*[@type="Boolean"]') as $node) {
             // something to set the value of $node to the value of "True"
             }
    echo $dom->saveXML();

我试过：

$node->{0} = value; // does not actually replace values but doesn't error
$node[0] = value; // errors  Cannot use object of type DOMElement as array

另外，如果有人知道，我如何告诉DOM不要使用简写输出XML？