bug#26650: 26.0.50; Protect *Backtrace* from accidental killing

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Eli Zaretskii <eliz@gnu.org> writes:

>> >> +  (add-hook 'kill-buffer-hook
>> >> +            (lambda () (if (> (recursion-depth) 0) (top-level))) nil t)
>> >
>> > This will throw to top-level when _any_ buffer is killed, as long as
>> > we are in recursive-edit, no?
>> No, because `add-hook' is called with non-nil LOCAL arg.
>
> Right, sorry for not paying attention.

Maybe I should have written

    (add-hook 'kill-buffer-hook (lambda ...) nil 'local)

to emphasize this?  I'm still undecided on the general style question of
whether to use t or '<symbol> in these cases.