bug#27584: 26.0.50; alist-get: Add optional arg TESTFN

[Eli Zaretskii <eliz@gnu.org>]

> From: Nicolas Petton <nicolas@petton.fr>
> Cc: tino.calancha@gmail.com, 27584@debbugs.gnu.org, monnier@iro.umontreal.ca
> Date: Tue, 01 Aug 2017 18:49:43 +0200
> 

A few comments:

> * doc/lispref/lists.texi: Document the change.

This should state the node in parentheses (as if it were a function).

> +@defun rassoc value alist &optional testfn
>  This function returns the first association with value @var{value} in
> -@var{alist}.  It returns @code{nil} if no association in @var{alist} has
> -a @sc{cdr} @code{equal} to @var{value}.
> +@var{alist}, comparing @var{value} against the alist elements using
> +@var{testfn} if non-nil, or @code{equal} if nil (@pxref{Equality

The "if nil" part is confusing, because you actually mean "if
@var{testfn} is nil".

Also, "nil" should be in @code.

> +Predicates}).  It returns @code{nil} if no association in @var{alist}
> +has a @sc{cdr} equal to @var{value}.

That reference to cdr is a surprise.  the original description talked
about cdr right from the start, but the new one doesn't.

Thanks.