anchor.diff:  
   -export([start_link/0]).
   
  --export([register_watcher/1,
  +-export([watchers/0,
  +         register_watcher/1,
            unregister_watcher/1]).
   
   %% gen_event callbacks
  
positive.code:                                              {?MODULE, ns_node_disco_events},
                                               ns_node_disco_events)
                      end)}.
  
  register_watcher(Pid) ->
      gen_event:call(ns_config_events,
  
negative.code: handle_event(_, State) ->
      {ok, State}.
  
  handle_call(watchers, #state{watchers = Watchers} = State) ->
      {ok, Watchers, State};
  
  handle_call({register_watcher, Pid},
              #state{watchers = Watchers} = State) ->
      Watchers2 = case lists:keysearch(Pid, 1, Watchers) of
  