Want to develop plugins for IPython Notebook editor, where to start?

I have some experiences on developping plugins for the intellij platform. I plan to write a new plugin for the IPython Notebook editor, but I don't know where to start. 

I found this directory in the intellij source code repo: https://github.com/JetBrains/intellij-community/tree/master/python/ipnb, which indicates there should be some classes named IpnbPy* in the pycharm sdk. But I didn't found these classes inside pycharm.jar. I tried the PsiViewer plugin, but it doesn't work in the IPython Notebook editor, while it does work for normal *.py files.

Could you please tell me where should I start?