I'm browsing through some of Electrum's default plugins in the /plugins directory. It looks like plugins hook into Electrum using @hook annotation, as in this method from audio_mode:

@hook
def transaction_dialog(self, dialog):
    b = QPushButton()
    b.setIcon(QIcon(":icons/speaker.png"))

https://github.com/spesmilo/electrum/blob/master/plugins/audio_modem/qt.py

Where can I find Electrum 3 API documentation for writing plugins such as a list of all hook function names and the arguments they take?