bug#15748: 24.3.50; `customize-group': Provide a way to hide/show all values

[Eli Zaretskii <eliz@gnu.org>]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: hmelman@gmail.com,  15748@debbugs.gnu.org
> Date: Wed, 11 May 2022 13:44:20 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Thanks, but can we have some documentation about its usage?  For
> > starters, in which buffers it is supposed to be used, and how?  I
> > thought this was for the buffer created by customize-group, but there
> > it seems I can use 'H' only once: after that one time, which reveals
> > all the variables, any subsequent 'H' press says "Invalid widget type"
> > and does nothing.  (I used the buffer created for the 'display' group,
> > in case it matters.)
> 
> Yes, it matters -- I was testing in a group with a different widget
> selection, so I didn't see this bug.  Now fixed on the trunk.

It now works in "*Customize Group*" buffers I tried, but the problem
is still there in some other similar cases.  For example, try

  M-x customize-apropos RET window RET

In the resulting buffer, the second 'H' still gets the same Invalid
widget error.  The same happens in a buffer created by
customize-faces.

Also, what about "M-x customize-browse"?  The buffer looks
differently, but don't we want 'H' to do the same there?

> > I tried to understand whether I did something wrong by reading the doc
> > string of the new command, but it didn't add anything to my
> > understanding; it doesn't even say which "widgets" is it talking
> > about.
> >
> > I think we need to improve the user documentation of this new feature.
> 
> It just toggles the visibility, like that arrow thing.  I don't know
> what further can be said.

I've now made the doc string more detailed.