The ajax() method doco here: http://api.jquery.com/jQuery.ajax/ indicates that the "data" parameter handles arrays by creating multiple request params with the same key name, and gives an example: {foo:["bar1", "bar2"]} becomes '&foo=bar1&foo=bar2'.

That is exactly how I would expect multiple values for the same key to be submitted, and it did work like this in version 1.3.2. However, I recently upgraded to jQuery version 1.4.2 and now my ajax calls don't work. Debugging on the server side, I find that for the above example instead of creating multiple request params with the specified key name of "foo", jQuery is creating the request param as "foo[]" (with the square brackets part of the name). Not having time to clarify just what jQuery is doing, and certainly not having time to change all my existing code, I had to go back to jQuery 1.3.2 where the ajax calls work beautifully.

In searching to see if this has previously been reported I found a ticket or two from people who seemed to want square brackets on their parameter names, but I disagree that this is a good idea (surely if there is a good reason to want that on the server side you can just code it as "foo[]" in the client ajax call?) and in any case if this new behaviour is on purpose please update the doco to match.