如何将XML字符串附加到DOMDocument对象？

Creating the DOMDocument object:

$getToken = '<getToken>...</getToken>';
$getToken_objeto = new DOMDocument("1.0", "UTF-8");
$getToken_objeto -> loadXML($getToken);

Trying to append a XML string (Signature) into the DOMDocument created above:

$Signature = '<Signature>...</Signature>';
$Signature_objeto = new DOMDocument("1.0", "UTF-8");
$Signature_objeto -> loadXML($Signature);
$Signature_nodeList = $Signature_objeto -> getElementsByTagName("Signature");
$Signature_node = $Signature_nodeList -> item(0);
$getToken_objeto -> importNode($Signature_node, true);
$getToken_objeto -> appendChild($Signature_node);

I get 2 errors:

Fatal error: Uncaught exception 'DOMException' with message 'Wrong Document Error' in C:... DOMException: Wrong Document Error in C:...

Seems simple to resolve but im quite unexperienced using the PHP DOM extension.

Thanks in advance.

You're trying to append the original node - not the imported one.

$Signature_node = $getToken_objeto->importNode(
  $Signature_nodeList->item(0), true
);

You're trying to append the node to the document, but an XML document can only have a single document element and it already has one. You can append it to the document element:

$getToken_objeto->documentElement->appendChild($Signature_node);

But PHP can load XML fragments directly into a DOMDocumentFragment.

$xml = '<getToken>...</getToken>';
$fragmentXml = '<Signature>...</Signature>';

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

$fragment = $dom->createDocumentFragment();
$fragment->appendXml($fragmentXml);

$xpath
  ->evaluate('//getToken')
  ->item(0)
  ->appendChild($fragment);

echo $dom->saveXml();