@yyr You are right, thank for the info.

How about `C-,` or `C-*`?  Both are empty in plain Emacs. I took `C-.` from `M-.` of SLIME.  SLIME binds `M-,` (and `M-*`) for pop so I think it makes sense.

(Stricktly speaking we should bind `C-c` + punctuation for minor mode but that's why I am not enabling it by default anyway.)