It took an incredibly complex and gross implementation to produce
the simple grab effect described above.
Given the current implementation, it isn't safe for applications
to use the Xlib grab facilities at all except through the Tk grab
If applications try to manipulate X's grab mechanisms directly,
things will probably break.
If a single process is managing several different Tk applications,
only one of those applications can have a local grab for a given
display at any given time. If the applications are in different
processes, this restriction doesn't exist.