Major Section: HISTORY
Example: :ubt! :x-4
The keyword command :ubt! is the same as :ubt, but with
related queries suppressed appropriately, and with a guarantee that it is
``error-free.'' More precisely, the value returned by :ubt! will always
be of the form (mv nil val state). :Oops will undo the last
:ubt!. See ubt, see ubu, and see u.
