@unwarlikeExtortion Sure - what additional things would you like accessible via API? Public docs for reference: https://developer.gimp.org/resource/api/

As for separation, the styling of elements is done via separate (GTK3 subset of) CSS so that's fairly flexible. The GUI elements themselves are defined in C, which is less flexible but we do separate them out in source in our /widgets and /gui folders as best we can.