It's often desirable for UI to be described in a declarative fashion, i.e. instead of where you have "do something" (set button color to red), refactoring so it

It's often desirable for UI to be described in a declarative fashion, i.e. instead of where you have "do something" (set button color to red), refactoring so it becomes "is something" (button is red if state is x) I might not be describing that well, because once you go down that road it really becomes a whole overall approach that infects the whole program (like functional reactive programming), and so it's really about how the whole flow fits together from top to bottom, and that can be very elegant. I don't think that's the right fit for everything, i.e. in gamedev it might make more sense to just update some object's position imperatively, but for UI it tends to work pretty well.