如何更改XML节点值？

Question

I've reviewed numerous posts on this topic and have tried to make adjustments to my code but can not seem to make it work, any help is greatly appreciated.

How do I update the value of cen_inst_units_z_name?

XML

<?xml version="1.0" encoding="UTF-8" ?> 
<xfa:data xmlns:xfa="http://www.xfa.org/schema/xfa-data/1.0/">
    <form1>
          <cen_inst_units_z_name>Department of School</cen_inst_units_z_name>
    </form1>
</xfa:data>   

PHP

<?php 
    $doc = new DOMDocument();
    $doc->load('52500_data.xml');
    $xpath = new DOMXPath($doc);

    $parent = $doc->getElementsByTagName('form1')->item(0);
    $query = $xpath->query('cen_inst_units_z_name',$parent);

    //Checked to make sure I was pulling the correct node
    echo $query->item(0)->textContent;

    $query->item(0)->nodeValue = 'Test123'; 
    $doc->saveXML();
?>

Answer 1

I changed code to save a new document and got the result I was looking for:

$doc->save("newdoc.xml");