According to the documentation, the settings element in a GUI editor (or model) config file can contain an element called customconfiguration (see http://docs.sdl.com/LiveContent/content/en-US/SDL%20Tridion%20full%20documentation-v1/GUID-ACE0B7E2-31DC-40CC-BEC5-B3D6FD76EDE5).
I suppose I can enter my own configuration settings there. But what's not clear to me is how these settings should be formatted and how I can use them in my code. Can anyone point me in the right direction?