Comment by Philpax

I look at the Nix definition for the relevant module as you often need to see what it's actually doing in order to understand it (yes, it's one of those ecosystems).

For example, for the `steam` program (not package - the package is a dummy): https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/p... and then look for "lib.mk".