I might be imagining this but I think that I have seen ligatures on/off being used as a deliberate hint to convey the difference between read-only and editable

I might be imagining this but I think that I have seen ligatures on/off being used as a deliberate hint to convey the difference between read-only and editable code. That's a very nice tweak. InteliJ at least can be configured that way, might be a case where its Android Studio incarnation has different defaults.