I think something like:
Also documented in the >Emacs user's manual<.
Also documented in the >ELisp programmer's reference<.
should be clear enough (where >...< is meant to delimit the hyperlink).
That won't help with functions (vars, faces, etc.) covered in other
manuals: CL, Tramp, Org, Dired-X, Calc, Ediff, etc.
Why not? I'd expect them to appear as things like:
Also documented in >Calc's manual<.
I meant that it won't help now (as is, with `Info-lookup').
Yes, links to such manuals would help.
But if we are going to do this for more, or all, names referred to in
*Help*, and not just for the name that's the subject of the *Help*, then
"Also documented in..." would become a real drag.