Variable: comment-add
comment-add is a variable defined in newcomment.el.gz.
Documentation
How many more comment chars should be inserted by comment-region.
This determines the default value of the numeric argument of comment-region.
The plain comment style doubles this value.
This should generally stay 0, except for a few modes like Lisp where it is 1 so that regions are commented with two or three semi-colons.
Source Code
;; Defined in /usr/src/emacs/lisp/newcomment.el.gz
(defvar comment-add 0
"How many more comment chars should be inserted by `comment-region'.
This determines the default value of the numeric argument of `comment-region'.
The `plain' comment style doubles this value.
This should generally stay 0, except for a few modes like Lisp where
it is 1 so that regions are commented with two or three semi-colons.")