How to insert text in the parent node just before a child node in PHP DomDocument

Question

I have this XML:

<p>
     This is a test <xref>1</xref> in the XML <xref>2</xref> bla bla bla....
</p>

What I would like to do is to add the letter "N" just before the <xref>

For that, I tried to use DOMNode::insertBefore but without success.

Ex:

$refs = $paragraph->getElementsByTagName("xref");

foreach ($refs as $key=>$ref) {
   if ($key == 0) {
      $N = $dom_input->createTextNode("N");
      $citation->insertBefore($N);
   }
}

But the N text node is not inserted.

Thank you in advance for your help.

Answer 1

I was able to fix the problem. I did a mistake, the code should look like:

if ($key == 0) {
    $squareBracket = $dom_input->createTextNode("[");
    $paragraph->insertBefore($squareBracket, $citation);
}