bug#29838: 26.0; Elisp manual: describe standard-error sexps

[Drew Adams <drew.adams@oracle.com>]

> >
> > Please explain whatever _can_ be explained.
> 
> Sorry, I don't know how to do that in any useful way.  Maybe someone
> else will have an idea.

As I said:

  A start could to be to mention that an `args-out-of range'
  error sexp has the form `(args-out-of-range ARG...)' or
  whatever the truth is, and then say what ARG represents,
  in general terms.

And as I said:

  If [users] saw only nice error messages such as "Args out
  of range: [1 2 3 4], -1" then there would be no such problem.

That too would take care of this bug.

Put differently, users should not see a message that refers
to something (internal?) that they cannot understand and
that you say you don't know how to explain.  But that's
what happens currently with (as one example), errors raised
on `post-command-hook'.

It is presumably possible to see such unhelpful messages
also in other contexts where raising an error is suppressed
in favor of showing a message about the error.  Perhaps a
all such inferior messages could be fixed at the same place
(dunno).