RE: Emacs's handling of line numbers [from bug#5042]

[Drew Adams]

> It would perhaps be useful to distinguish between user narrowing and
> program narrowing (the one used by Info, rmail, etc., I mean). Or, put
> it other way, perhaps we need a narrowing facility for elisp code,
> separate and independent from the user widen/narrowing interactive
> command set.

[I suspect that the following is not what Mark has in mind, and if so then I
don't want to divert attention from his questions - I'll drop it (or start a
different thread if there is any interest).] 

One thing I've sometimes thought would be handy is an additional widening
command, `widen-one-level', which would widen only as far as the next-to-last
narrowing. 

You can narrow and then narrow further, any number of times. But `widen' always
widens completely. Sometimes I would like to just undo the last level of
narrowing, returning to the previous level (or to the top level, if there is
only one narrowing).

This would require managing a list or stack of narrowing limits etc.

I have no idea whether anyone else would find such a command useful. And I can't
really characterize useful use cases. But I know I've sometimes wanted such a
feature.