Nixos octoprint plugin option function help

I am trying to set up an octoprint instance with plugins and it expects the following option:

services.octoprint.plugins = plugins [ plugins.stlviewer ];

I was wondering, where is the stlviewer member of plugins defined?
Or how can I see a list of all members? Maybe using nix repl?

I tried to reverse engineer it a little.
I found that it builds a derivation of the octoprint packages python version, which gets its packages from:


Now I have the problem that I cannot install pip into the octoprint environment, but I will create another tread for that.