ring the grab.
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Two forms of grabs are possible:  local and global.
A local grab affects only the grabbing application:  events will
be reported to other applications as if the grab had never occurred.
Grabs are local by default.
A global grab locks out all applications on the screen,
so that only the given subtree of the grabbing application will be
sensitive to pointer events (mouse button presses, mouse button releases,
pointer motions, window entries, and window exits).
During global grabs the window