The sad this is, that this whole specification is centered about the classical stacked window management paradigm and the assumption, that one window can be pla

The sad this is, that this whole specification is centered about the classical stacked window management paradigm and the assumption, that one window can be placed at only one screen at a time. However given modern compositing WM methods it was perfectly possible (and is implemented by experimental WMs) to place windows independently on multiple screens.