RE: Why there is no key in the *Help* buffer to bring up the relevant info page?

[Drew Adams <drew.adams@oracle.com>]

> > You might be interested on this: <helpful.el>
> Yes, thank you, I found it recently and it seems more featureful than
> the built in Help. Maybe the author should be asked to sign FSF papers
> if he hasn't yet done so and submit his code to replace the default
> Help.

What you request was discussed very recently on
emacs-devel@gnu.org.

I wrote this there:

----

 Since 2011 library `help-fns+.el' has had that feature.

 And it's user configurable - not just on/off, by
 option `help-cross-reference-manuals':

 1. Choose the list of manuals to search. Default:
    Emacs and Elisp manuals.

 2. Choose whether to (a) search systematically,
    when `*Help*' is created, and add a `manuals'
    link only if search finds hits, or (b) always
    create a link, and search only when the link
    is followed.  Default: (b).

https://lists.gnu.org/archive/html/emacs-devel/2019-07/msg00242.html

This feature is implemented by searching the
manuals listed in a user option.  By default,
the manuals are Emacs and Elisp.  But you can
choose any Info manuals you like.

Now if Emacs itself implemented such a feature
then there might presumably be no need to search
for the right manual location(s) to visit either
(a) when you display the *Help* that contains the
link or (b) when you click the link.

Emacs itself could perhaps have an internal table
that gets populated at build time - at least for
manuals such as Emacs and Elisp.

And if more manuals were chosen by a user (by such
an option) then those additional manuals could be
handled similarly to what `help-fns+.el' does now:
user choice whether to search (a) when *Help* gets
displayed (slow, and useless if there's no match)
or (b) only when you click the link for Info.

Note that the `help-fns+.el' implementation adds
a single link in *Help*.  When followed, if there
are hits in both Emacs and Elisp then it goes to
an Info buffer that has a links to each of those
manuals.  (If only one manual covers it then the
link takes you directly to that location.)

https://www.emacswiki.org/emacs/download/help-fns%2b.el