How do I get the entire XML string from a XMLDocument returned by jQuery (cross browser)?

I have tried and failed to find out how to get the entire XML string from the XMLDocument returned by a GET. There are a lot of questions on SO on how to find or replace specific elements in the object, but I can't seem to find any answer to how to get the entire document as a string.

The example I'm working with is from here. The "do something with xml"-part is where I'm at at the moment. I get the feeling that this should be really trivial, but I fail to find out how. Is there an "xml.data()" or similar that can be used for this purpose?

$.ajax({
    url: 'document.xml',
    type: 'GET',
    dataType: 'xml',
    timeout: 1000,
    error: function(){
        alert('Error loading XML document');
    },
    success: function(xml){
        // do something with xml
    }
});

The use case is that I want to feed the xml to flash plugin and for that I need the actual XML as a string.