PHP XMLReader获取父节点？

$xml = '<root><parent<child>Text</child></parent></root>';
$reader = new XMLReader();
$reader->XML($xml);

// 遍历到子节点
while ($reader->read()) {
    if ($reader->nodeType == XMLReader::ELEMENT && $reader->name == 'child') {
        // 获取子节点的父节点
        $parentNode = $reader->expand();
        // 获取父节点名称
        $parentNodeName = $parentNode->name;
        echo "Parent node name: " . $parentNodeName . PHP_EOL;
    }
}