Custom content-type converters in .ajaxSetup() also needs a "contents" map entry

$.ajaxSetup({
    converters: {
        "mycustomtype json": function (result) {
            //do stuff
            return newresult;
        }
    }
});

was not working. The solution needed was:

$.ajaxSetup({
    contents: {
        mycustomtype: /mycustomtype/
    },
    converters: {
        "mycustomtype json": function (result) {
            //do stuff
            return newresult;
        }
    }
});

which simply included a contents regex map. Please see http://bugs.jquery.com/ticket/11376 for more information, and ping @addyosmani to see if he's attempted documenting this yet.

Start by reviewing the jQuery ajaxSetup documentation and the linked ticket 11376. Document that custom content-type converters also require a matching contents regex map, using the example from the issue; done means the relationship between contents and converters is clear to readers.