bug#21315: 25.0.50; doc of `kill-ring-save', `copy-region-as-kill' - bad

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 5 Dec 2015 18:13:37 -0800 (PST)
> From: Drew Adams <drew.adams@oracle.com>
> Cc: 21315@debbugs.gnu.org
> 
> > > At least make clear that what is said about REGION is only
> > > for calls from Lisp.  REGION is always non-nil when used
> > > interactively.
> > 
> > Maybe REGION should be non-nil only when used on a non-contiguous
> > (rectangular) region?
> 
> Maybe; dunno.  The doc is not clear; that's all I can tell.

Would it become clear if instead of this:

  The optional argument REGION if non-nil, indicates that we're not
  just copying some text between BEG and END, but we're copying the
  region.

it would say this:

  The optional argument REGION non-nil means to ignore BEG and END and
  copy the region instead.

Also, we should tell that this distinction is only relevant to
invoking these functions from Lisp programs, not interactively.

As for the argument, AFAICT it makes no difference in interactive
usage.  kill-region make it very clear:

    (interactive (list (mark) (point) 'region))

Does documenting the above clarify the issue?