anchor.diff:  	 max_files/0,
   	 max_peers/0,
   	 max_upload_rate/0,
  +	 max_download_rate/0,
   	 max_upload_slots/0,
   	 optimistic_slots/0,
   	 profiling/0,
  
positive.code: -spec optimistic_slots() -> pos_integer().
  optimistic_slots() -> call(min_upload).
  
  -spec max_upload_rate() -> pos_integer().
  max_upload_rate() -> call(max_upload_rate).
  
  -spec listen_port() -> pos_integer().
  listen_port() -> call(port).
  
negative.code:      optional(fs_watermark_high, 128),
       optional(max_upload_slots, auto),
       required(min_upload),
       optional(max_upload_rate, infinity),
       optional(max_download_rate, infinity),
       required(port),
       required(logger_dir),
       required(logger_fname),
  