Parsley ships with a lot of easy to use built-in stuff, be sure to read the doc!. In some cases, you'll need to work more deeply with listeners, internals.. If you're stuck, have a look at StackOverflow's great Parsley questions and answers.
If you are either pretty sure that you spotted a vicious bug, or have a great feature implementation / idea, be sure to go to GitHub and open an issue or a pull request.