Pretty much the full web dev stack is open source, including jQuery. If you really get stuck, you'll actually learn more by reading the source code than by getting a piecemeal info on Stackoverflow. I don't remember having to do that with jQuery (most of the JS I write is without a JS library, and I have the rhino book), but I've frequently read the source code to bits of Rails or MRI when I've not understood something and been offline.
Yeah you definitely can glean a fair bit from the source, something like selectors is fairly verbose though as it is a parser so often it's far quicker just to Google up the specific thing you need. You can also get a deeper understanding from the source so it does probably balance out.
