A tiny comment that might make the Javascript code a bit more understandable to mere humans: in Javascript, '$' is a normal character for variable names. So in this example, $ is the name of a function, most likely defined in the (Javascript) library loaded by your Perl library, and I assume it does something along the lines of document.getElementById. Probably.

update I've tested it interactively in Firefox (with Firebug), on this site, and $ is a defined function. Weird. I don't know how standard it is, I had never heard of it before, so I'm not absolutely works in other browsers, but it is apparently indeed a shortcut for document.getElementById(id). But, it's a pretty hard "word" to Google for...

update Found it. It apparears to be defined in the Prototype library, and I think some extension I have loaded must depend on it.