is a variable defined in `
C source code
Its value is
- Automatically becomes buffer-local when set.
- This variable may be risky if used as a file-local variable.
- This variable is safe as a file local variable if its value
satisfies the predicate `null'.
Function called (if non-nil) to perform auto-fill.
It is called after self-inserting any character specified in
the `auto-fill-chars' table.
NOTE: This variable is not a hook;
its value may not be a list of functions.