title: Why is setting the innerHTML not working?
body: <p>My xml document is this:</p>
  
  <pre><code>&lt;Order&gt;
    &lt;size width="16.5" height="19.5"&gt;
      &lt;width&gt;16.5&lt;/width&gt;
      &lt;height&gt;19.5&lt;/height&gt;
    &lt;/size&gt;
    &lt;type&gt;photo&lt;/type&gt;
    &lt;/overlay&gt;
    &lt;Mats&gt;&lt;/Mats&gt;
    &lt;Openings&gt;&lt;/Openings&gt;
    &lt;Moulding&gt;&lt;/Moulding&gt;
    &lt;Glass&gt;&lt;/Glass&gt;
  &lt;/Order&gt;
  </code></pre>
  
  <p>I am trying to fill in the values of the Mats tag.
  Here is my javascript code:</p>
  
  <pre><code>function common_get_order_xml()
  {
    var parser = new DOMParser(); //create a new DOMParser
    var doc = parser.parseFromString(common_get_common_order_xml(), "application/xml"); //convert the string to xml
    console.log(doc); //outputs what is above
    //doc.getElementsByTagName('Mats').innerHTML = mattes_get_mattes_xml().replace("&lt;Mats&gt;", "").replace("&lt;/Mats&gt;", ""); //add the mattes
    doc.getElementsByTagName('Mats').innerHTML = "TEST";
    doc.getElementsByTagName('Openings').innerHTML = mattes_get_openings_xml(); //Add the openings
    doc.getElementsByTagName('Moulding').innerHTML = moulding_get_moulding_xml(); //Add the moulding
    doc.getElementsByTagName('Glass').innerHTML = glazing_get_glass_xml(); //Add the moulding
    var serializer = new XMLSerializer(); //create a new XMLSerializer
    common_order_xml = serializer.serializeToString(doc); //convert the xml back to a string
    return doc;
  }
  </code></pre>
  
  <p>But when I output doc, the Mats innerHTML does not get set to "TEST"</p>