This is the issue with imposing semantics of the programming model on the behaviour.

User behaviour is the only _real_ thing, it happens. Everything else is in your head. If people in the real world use PiP, then it should happen. The programming model has to bend and change to support it. It simply does not matter if the window manager does something or the window does something.

Sure, there is always the security argument wayland folks fall back to. But what ever is the problem with making a one-time permission popup? "Google Chrome wants to open in PiP: allow | allow once.". Just expose the existing PiP code in the window manager as an API guarded with an `if` that apps can call. It's not even that much real work, just pure bikeshedding and architecture astronauting.