.responseXML DOM Methods not working

[seniseven]

I am requesting and getting in the response of the XML HTTP request object
text that gets parsed correctly into XML (using Firefox). The
Firebug debugger shows

• I can traverse the document using firstChild, nextSibling properties
• DOM methods for the document object are present, but are not returning expected results
  * I have the following code:
  
  var docFrag = XmlHttpRequestObject.responseXML;
  
  I then used it to get values from the debugger shown below

docFrag.documentElement: [DomNode] ajaxresponse
docFrag.getElementById("div1"): [null]
docFrag.documentElement.getElementById: [undefined]
docFrag.getElementById: [method (func ref)] getElementById()
x = docFrag.firstChild: [DomNode] ajaxresponse
x.nodeName: [string] "ajaxresponse"
x.nodeType: [number] 1
y = x.firstChild.firstChild: [DomNode] div
y.nodeName: [string] "div"
y.nodeType: [number] 1
y.getAttribute: [method (func ref)] getAttribute()
y.id: [undefined]
y.getAttribute("id"): [string] "div1"


The bracketed part is the Javascript type of the value returned

Note that there is a node (element div) with an id attribute of div1,
and there is a getElementById() method in the XML document object
(docFrag), as found by getAttribute() method on the node, but
getElementById() returns null.

Can anyone resolve these inconsistent expectations?

For additional information, I have provided the unformatted HTTP response
text and the parsed XML content below.

HTTP Response Text

<?xml version="1.0"?>
<ajaxresponse><peptide><div id="div1" style="font:normal 90% 'Courier New',Tahoma,monospace;color:red;">&#xD;
This is the content of Div1.  And just for variety, we include some complex&#xD;
elements like a <b>table</b> and a style attribute.&#xD;
<table><tr><th>Header 1 </th><th>Header 2&#xD;
</th></tr><tr><td>A table </td><td>with three cells </td><td>in a row&#xD;
</td></tr><tr><td colspan="3">Oh, and also with two rows, the 2nd with three column span&#xD;
</td></tr></table></div></peptide><metal><div id="div2">&#xD;
<p>&#xD;
A more modest DIV with a text containing a paragraph element&#xD;
</p></div></metal></ajaxresponse>

XML as Parsed

<ajaxresponse>
 <peptide>
  <div id="div1" style="font:normal 90% 'Courier New',Tahoma,monospace;color:red;">
   This is the content of Div1. And just for variety, we include some complex elements like a
   <b>table</b> and a style attribute.
   <table>
    <tr>
     <th>Header 1 </th>
     <th>Header 2 </th>
    </tr>
    <tr>
     <td>A table </td>
     <td>with three cells </td>
     <td>in a row </td>
    </tr>
    <tr>
     <td colspan="3">Oh, and also with two rows, the 2nd with three column span </td>
    </tr>
   </table>
  </div>
 </peptide>
 <metal>
  <div id="div2">
   <p>
   A more modest DIV with a text containing a paragraph element
   </p>
  </div>
 </metal>
</ajaxresponse>

[seniseven]

I think my first post is a victim of too much information, which made my simple question seem overly complex.

This is simple. I get the responseXML property back.

I see it in my debugger. The property points to a DOM object. It has the method getElementById() among others. But the method is not returning the <div> DOM node with 'id' attribute, although it is there!

Anyone?