is a variable defined in `
Its value is
- Automatically becomes buffer-local when set.
String that starts line comments, or nil if such don't exist.
Line comments are always terminated by newlines. At least one of
`c-block-comment-starter' and this one is assumed to be set.
Note that it's currently not enough to set this to support a new
comment style. Other stuff like the syntax table must also be set up