bug#30241: Emacs 26.0.91: "Generalized variables" are not defined.

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

> > > I think you'll see a difference - it is, IMO, "significantly
> > > different".
> 
> > Actually, no, I didn't.  I do see some additional explanations that
> > might have helped Alan understand the issue, but nothing
> > "significant".  So much so that I doubt Alan will find the CL docs
> > helpful after disliking our docs of the same subject, as he did, based
> > on his original bug report.  Of course, it's possible that I'm missing
> > something here.
> 
> > Therefore, I invite Alan (and anyone else who'd like to chime in) to
> > please compare the CL docs on this matter with ours, and tell what
> > parts of the former made the issue "fall into place" (pun intended)
> > wrt this topic, where our docs don't.  Bonus points for proposing
> > patches for the relevant parts of the ELisp manual, to make this
> > subject's documentation "significantly" better.
> 
> I've read...,
> and found it clear indeed.  However it was also long.  After reading it,
> the Elisp sections on generalised variables make much more sense.
> 
> This suggests that these Elisp sections contain the material, but are
> not suitable for readers who don't already understand generalised
> variables.
> 
> In that CL page, a generalised variable is effectively defined as
> something you can use `setf' on within the first three paragraphs.  In
> the elisp sections, that identification is not present in the opening
> paragraphs - there is no definition on that opening page.  The first
> sub-page does not define a generalised variable as something you can use
> setf on - it merely says setf is a way to access one.  But that
> definition needs to be in the top level page, and it needs to be clear
> that it _is_ a definition.
> 
> The CL page gives a complete list of forms setf will work with.  The
> elisp page merely gives a list, without it being clear whether that list
> is complete or not.

Good summary.  FWIW, I agree.  It's about `setf', in particular.