Electrum Plugin development

Hi - I'm interested in developing a plugin for Electrum.

Is there any documentation on where to start with this? I've cloned she github repo on my local machine, and can compile and run everything. There's a plugins folder, and I've looked through there. Can I just put any old .py file in there? I haven't found any guide / HOWTO / readme or anything about the plugins, is there anything and I've missed it?

So far I've tried to duplicate the "virtual keyboard" plugin, to make a "bad keyboard" which only has the letter A. Copying and modifying the virtualkeyboard.py file works, and I get a checkbox in the plugins menu in electrum. It seems to work and I can modify it, but is there any defined API? Do I have to modify other files in the lib folder and so on, or should I be able to do everything I need to from the plugins folder?

I'm looking into making some client side multi-sig stuff and thought the idea of Electrum plugins seemed promising. If there are other bitcoin clients anyone things might be more suitable or modifiable I'm also open to those suggestions before I get to deep into the Electrum codebase (which is a great project, but I'm hoping with a plugin I can leave that side unmodified)

Thanks for any info / links / help