Anyone use the PAJAX Framework?

Hello,

I downloaded and began experimenting with the PAJAX framework and I
think it's a pretty cool way of doing AJAX to backend PHP scripts.
However, I'm not quite understanding how I can get XML data from a PHP
function that returns XML. Normally with AJAX I would use something
like "var xml = request.responseXML". How can I get XML data with
PAJAX?

Also, can someone describe how to use JSON in the context of PAJAX?