RE: `declare-function' docu

[Drew Adams]

> > Here we see the benefits of links from the docstring-based
> > help system to the info pages, which IMO should always be
> > present when available. When this issue was brought up last
> > time around, there was the argument that links would increase
> > the size of Emacs.
> 
> For anyone that doesn’t know and is interested, there is the package
> ‘helpful’[1] on MELPA which provides (among many other things) links to
> the info manuals from its ‘*help*’ buffers.
> 
> (describe-package 'helpful)
> 
> [1]
> https://urldefense.com/v3/__https://github.com/wilfred/helpful__;!!Gqiv
> PVa7Brio!PvV817f2RWtnUCodAGybbqf0ieslwKXhTIpY4ie5T7VwmIPQytGCQCwFEkrnNe
> AB$

Similarly, help-fns+.el.
There you have option `help-cross-reference-manuals':

 `help-cross-reference-manuals' is a variable defined in `help-fns+.el'.
 Its value is (("emacs" "elisp"))

 Documentation:
 Manuals to search, for a `*Help*' buffer link to the manuals.
 A cons.

  The car is a list of manuals to search, or the symbol `all', to
   search all.  If nil, then do not create a cross-reference link.

  The cdr is a boolean:

   Non-`nil' means search the manuals, then create a cross-ref link:
         create it only if some search hits are found.

   `nil' means create a cross-ref link without searching manuals
         first (but only if there are some manuals to search).

You can customize this variable.

---

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