PHP XPath检查是否为空

$xml = <<<XML
<root>
  <node1></node1>
  <node2>Some text</node2>
  <node3>
    <subnode></subnode>
  </node3>
</root>
XML;

$dom = new DOMDocument();
$dom->loadXML($xml);

$xpath = new DOMXPath($dom);

// 检查node1节点是否为空
$node1 = $xpath->query('/root/node1')->item(0);
if ($node1->childNodes->length == 0) {
    echo "node1节点为空\n";
} else {
    echo "node1节点不为空\n";
}

// 检查node2节点是否为空
$node2 = $xpath->query('/root/node2')->item(0);
if ($node2->childNodes->length == 0) {
    echo "node2节点为空\n";
} else {
    echo "node2节点不为空\n";
}

// 检查node3节点是否为空
$node3 = $xpath->query('/root/node3')->item(0);
if ($node3->childNodes->length == 0) {
    echo "node3节点为空\n";
} else {
    echo "node3节点不为空\n";
}