bug#47368: [External] : bug#47368: 28.0.50; map-elt returns nil without "deprecated" TESTFN

[Drew Adams]

> > This is expected, as alist keys are tested with eq by default.

Since when?  Where?  Expected by whom, and by what code?

> > That's what the docstring is trying to warn about: alists default to
> > testing with eq, but can also use eql, equal, or anything else.
> 
> Is it that obvious?  We have `assoc' and `assq' built-in - to me it's
> not obvious that "alist keys are tested with eq by default".  It's the
> default for `alist-get', ok, which is used by the implementation, but
> not everybody will know that.  I would add a sentence about that.

+1.

Alists are general.  They can be used in many ways.
Their keys can be tested in multiple ways.  Neither
code nor doc should assume anything about how an
alist is composed or treated - nothing beyond the
fact that at least some of the list elements are
likely to be conses.