comment-line-break-function is a variable defined in `simple.el'.
Its value is
comment-indent-new-line
This variable may be risky if used as a file-local variable.
Documentation:
Mode-specific function which line breaks and continues a comment.
This function is called during auto-filling when a comment syntax
is defined.
The function should take a single optional argument, which is a flag
indicating whether it should use soft newlines.