comment-start-skip is a variable defined in `newcomment.el'.
Its value is
This variable is safe as a file local variable if its value
satisfies the predicate `stringp'.
Regexp to match the start of a comment plus everything up to its body.
If there are any \(...\) pairs and `comment-use-syntax' is nil,
the comment delimiter text is held to begin at the place matched
by the close of the first pair.