The developer instructions are, basically, to read blox.py. It is very well commented, and you'll need to understand what it's doing in order to understand Cherry Blossom.

To figure out what each of the callbacks does, search for "cb_" inside the file, or look at all invocations of run_callback.

To write your own plugin, I recommend you check out the existing plugins. None are very long, and each does something different and relevant to understanding what's going on.

Finally, feel free to drop me a line at bill.mill at gmail.com to ask for help; I'll be glad to provide it.