<I>window</I>'s tree, button presses and
releases and
mouse motion events are reported to <I>window</I>, and window entry
and window exit events are ignored. The grab subtree
&#8220;owns&#8221;
the pointer:
windows outside the grab subtree will be visible on the screen
but they will be insensitive until the grab is released.
The tree of windows underneath the grab window can include top-level
windows, in which case all of those top-level windows
and their descendants will continue to receive mouse events
du