FWIW, the Plan 9 window system is in fact a (very barebones) compositor in modern terms, in that it (unlike classic X and like Wayland) maintains a backbuffer f

FWIW, the Plan 9 window system is in fact a (very barebones) compositor in modern terms, in that it (unlike classic X and like Wayland) maintains a backbuffer for every (top-level) window instead of communicating “damage” back to applications. That seems to be its very thing—there’s a distinct feeling of “look what computers let us do now” in the papers. I don’t think it knows anything about the widgets inside those windows, either (again unlike classic X and like Wayland). (On the other hand, like classic X and unlike Wayland, it makes the client funnel every drawing operation through the window system.)