Subject: 24.5; doc string of `self-insert-uses-region-functions'
From: Drew Adams <[email-masked]>
To: [email-masked]
Date: Mon, 20 Nov 2017 18:56:15 -0800 (PST)
List-Id: <debbugs-submit.debbugs.gnu.org>

Two lines of the doc string are too long.

The doc string is close to incomprehensible.

 Special hook to tell if `self-insert-command' will use the region.
 It must be called via `run-hook-with-args-until-success' with no arguments.
 Any `post-self-insert-command' which consumes the region should
 register a function on this hook so that things like `delete-selection-mode'
 can refrain from consuming the region.

HOW does this hook "tell if `self-insert-command' will use the region"?
What does a function on this hook need to do or return, to tell that?
And what does it mean for `self-insert-command' to "use the region"?

What does "any `post-self-insert-command'" even mean?  What is meant by
"consumes the region"?  Does "consume" mean the same thing in each
occurrence here?  What is meant by "registering" a function on a hook?

Is this ONLY about `delete-selection-mode'?  If not, what else is it
for?

A guess is that this is just a way to conditionalize the treatment of
`self-insert-command' by `delete-selection-mode'.  In some mode
(`electric-pair-mode'), you want to use a certain function as the value
of property `delete-selection' for symbol `self-insert-command'.

If so, then things would likely be clearer if that was said.

In that case, it needs to be understood that `delete-selection-mode'
checks the value of property `delete-selection' on
`self-insert-command', and if that value is nil or is a function that
returns nil then `delete-selection-mode' does nothing.

Say that, together with the fact that the function value of property
`delete-selection-mode' for `self-insert-command' runs the hook
functions in order, returning nil if any of them returns non-nil.

So a function on the hook should return non-nil when its aim is to
prevent deletion of the region by `self-insert-command'.  Say that.

Looking at the uses in the Emacs code, the aim seems to be only to
prevent deletion of the region by `delete-selection-mode' before
`self-insert-command' does its thing.  Whether `self-insert-command'
"uses" the region or "consumes" it, or even deletes it or ignores it, is
irrelevant, AFAICT.  All that matters is that this gives you a way to
decide conditionally whether `delete-selection-mode' deletes the region
on its pre-hook.

In GNU Emacs 24.5.1 (i686-pc-mingw32)
 of 2015-04-11 on LEG570
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/usr --host=i686-pc-mingw32'