What I find most interesting is that while XMLHttpRequest is at the core of this capability, your module actually doesn't need to generate or parse any XML at all!

Thank Google for that. I just tried to duplicate the interface, which is to take a string from the "qu" CGI parameter and to return some JavaScript code.

I started with a very simple CGI script, but then when I started writing another second one for another form I decided to put the common parts into a module (basically the JavaScript generation).