anchor.diff:  
   
   -define(TAB, ?MODULE).
  +-define(PID_INDEX, pid_to_name).
   
  --type monitors() :: [{reference(), binary()}].
   -record(state, {
  -	monitors = [] :: monitors()
   }).
   
   %%------------------------------------------------------------------------------------------------
  
positive.code: 
  %% API.
  -export([start_link/0]).
  -export([join_xnest/1]).
  -export([get_xnest_count/0]).
  
  %% gen_server.
  
negative.code: start_link() ->
  	gen_server:start_link(?MODULE, [], []).
  
  %% @doc Get the xnest by name, a new one will be created if the specfied is not exists.
  -spec get_xnest(binary()) -> {ok, pid()}.
  get_xnest(XNestName) ->
  	gen_server:call(?MODULE, {get_xnest, XNestName}).
  
  %% @doc Get current xnest number.
  -spec get_xnest_count() -> integer().
  