>> I can alt-click a window to move it in Xfree even if the application is blocking and I happen to click on a portion of the window that the application itself is responsible for drawing. Right?
>Right: that's server-side decoration.
No, that's window management. Decoration is just drawing borders around the window rectangle. in Wayland you still have a window manager, it's the compositor. The compositor does move windows around, hide or display them. It can do other things like distort them or map them to the sides of a spinning cube.
> a- client side decoration: the windows will be always displayed consistently even when resizing, but the animation may become jerky/unresponsive when resizing or moving if applications are slow to answer.
> b- server side decoration/management: moving or resizing windows will be animated smoothly but the content of a window when resizing can be "ugly" (incoherent) if the application doesn't answer fast enough.
As I said, the compositor can distort windows, so nothing prevents it from doing resizing the smooth and ugly way if needed. This will mean that, usually, applications will simple resize nice and smoothly, but if for some reason an application cannot resize fast enough, a good compositor can interpolate frames and keep the resizing smooth. It's the best of both worlds.
And again, this has nothing to do with decorations, but with window management. Currently the X11 window manager does both, but in Wayland those tasks are split between the application and the compositor.