bug#40916: [PATCH] Add "p" and "n" convenience bindings to help-mode-map

[Drew Adams]

> The following binds "p" to backward-button, and "n" to forward-button
> in help-mode-map for more conveniently jumping between buttons in *Help*
> buffers.  I have found myself constantly reaching for these in *Help*
> buffers after using helpful [0] for a while.

We already have TAB and S-TAB.  TAB has been
there forever, and S-TAB was added because it
was claimed to be "standard" or "conventional"
in some way.

And TAB and S-TAB are the same keys we use in
Info (where `n' and `p' move forward/backward
among node siblings).

Are we adding redundant keys now just because
someone gets used to them in some other app
or 3rd-party library?

Nothing prevents a user from binding `n' and
`p' that way.  And nothing prevents a library
from having a minor mode that binds them.

And Emacs not binding them by default means
they remain available for something else in
the future.