anchor.diff:  handle_message({ack, MessageClock}, State) ->
       partisan_acknowledgement_backend:ack(MessageClock),
       {reply, ok, State}.
  +
  +%% @private
  +schedule_distance() ->
  +    DistanceInterval = partisan_config:get(distance_interval, 10000),
  +    erlang:send_after(DistanceInterval, ?MODULE, distance).
   
   %% @private
   schedule_periodic() ->
  
positive.code: -type from() :: {pid(), atom()}.
  
  -record(state, {actor :: actor(),
                  vclock :: term(),
                  pending :: pending(),
                  membership :: list(),
  
negative.code:     %% Schedule periodic.
      schedule_periodic(),
  
      %% Schedule distance metric.
      schedule_distance(),
  
      %% Schedule periodic connections.
      schedule_connections(),
  
  