On 14/05/2018, Dave Horsfall <dave(a)horsfall.org> wrote (in part):
I had a boss once who demanded that we learn -mm; for
some reason I still
preferred -ms, as it somehow seemed more "natural", and I still use it to
this day (well, when I'm not using the Mac, that is).
Why not? The Mac has it: /usr/share/groff/1.19.2/tmac/s.tmac