Guys,
I am creating an XML doc from an nlapiRequestURL body.
like this :
var response = nlapiRequestURL(url, soapMess, headers, 'POST');
var rbody = response.body;
var xmls = nlapiStringToXML(rbody);

Using the debugger I can see I have :
xmls = {document} and nodes below it such:
   nodeName = {string} #document
   nodeType = {number} 9
   localName = null
   firstChild = {element} 
       nodeName = {string} soapenv:Envelope
       nodeType = {number} 1
       localName = {string} Envelope
[...]
So far so good.

I am unable to use methods on xmls such as xmls.nodeName
or
xmls.getElementsByTagName('Envelope'); (freaky return from this is : "org.apache.xerces.dom.DeepNodeListImpl@218e4130"!)

or using nlapiSelectValue.

I strongly suspect the xml document obj created by the nlapi call is anything but "standard".