anchor.diff:  %% @doc Decode state.
   decode(Active) ->
       sets:to_list(Active).
  +
  +%%%===================================================================
  +%%% reservation callbacks
  +%%%===================================================================
  +
  +%% @doc Reserve a slot for the particular tag.
  +reserve(Tag) ->
  +    gen_server:call(?MODULE, {reserve, Tag}, infinity).
   
   %%%===================================================================
   %%% gen_server callbacks
  
positive.code: handle_call({join, {_Name, _, _}=Node}, _From, State) ->
      gen_server:cast(?MODULE, {join, Node}),
      {reply, ok, State};
  
  handle_call(active, _From, #state{active=Active}=State) ->
      {reply, {ok, Active}, State};
  
negative.code:     Tag = partisan_config:get(tag, undefined),
  
      %% Reserved server slots.
      Reservations = partisan_config:get(reservations, []),
      Reserved = dict:from_list([{T, undefined} || T <- Reservations]),
      lager:info("Reserving slots for ~p", [Reservations]),
  
      %% Schedule periodic maintenance of the passive view.
      schedule_passive_view_maintenance(),
  