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Issue: EXIT-EXTENT (Version 6)

	    Version 5, 12-Dec-88, Mailed 12-Dec-88
Reason: MEDIUM provides more useful semantics in one important case: if
an application has a top-level catch tag, and a cleanup handler does a
(throw 'top-level ...) while cleaning up during such a throw.  Lack of
these semantics in Maclisp results in problems in Multics Emacs, whose
error handler prints a minibuffer message and then throws to the top
level, but if an error happens during a cleanup, the top-level catch is
no longer available, resulting in an infinite loop of "throw to
nonexistent tag" errors.  This seems like it would be a common paradigm,
but unless there is a way for a cleanup handler to determine the context
of its invocation, MINIMAL makes this non-portable.