> It may make sense to define a class of exceptions that cannot be
> caught by user provided handlers. This can include all exceptions a
> Scheme system raises where the standard just says "... it is an
> error". (*)

> The advantage of (*) is also that the danger inherent in the
> else-clause in the standard guard form would be diminished.

This could also be approached from the other direction by defining a new
`guard%` that catches absolutely everything, and implement the standard
`guard` so that it only catches "normal" high-level exceptions. If
necessary for conformance, the low-level exceptions can be called by
some other name than "exception".