Need to check 21.4.
Reported by Marcus Harnisch:
> Our d-c-r returns a coding system object like this:
> #<coding-system undecided undecided(do-eol do-coding) eol-type=lf>
(defun-when-void find-coding-systems-region (start end &optional buffer)
(detect-coding-system start end &optional buffer))))
> Also in contrast to the doc string d-c-r doesn't seem to return a list
> of these objects. At least not if there is only one coding system.
> The FSF function #'find-coding-systems-region returns an actual list
> of symbols, like (undecided). So it seems Aidan's response was
> correct, we don't have such a thing.