ermine which window in the
application receives the keyboard events.
The keyboard grab is released when the grab is released.
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Grabs apply to particular displays.  If an application has windows
on multiple displays then it can establish a separate grab on each
display.
The grab on a particular display affects only the windows on
that display.
It is possible for different applications on a single display to have
simultaneous local grabs, but only one application can have a global
grab on a given display a