[jQuery] The format of xml response
You are not sending down a Content-type: text/xml header, so the browser is
interpreting your XML as plain text.
To confirm this suspicion, change your alert to:
alert( xml );
You want the alert to display something like [object XMLwhatever]. Instead,
it will probably display the actual XML text. This indicates that it was
interpreted as plain text. Adding the header will fix that.
-Mike