anchor.diff:  -type user_attr() :: [{binary(), binary()}].
   % An 'internal' token is also used by internal consumers, but never stored.
   -type token() :: 'null' | binary().
  +-type tokentype() :: 'read' | 'write'.
   -type replyto() :: {pid(), reference()}.
   
   -record(tagcontent, {id :: binary(),
  
positive.code:             #state{delayed = {Waiters, OldUrls}, tag = Tag} = S) ->
      S1 =
          check_write_token(Token, ReplyTo, S,
                            fun() ->
                                do_delayed_update(Urls, ReplyTo, Waiters,
                                                  OldUrls, Tag, S)
                            end),
  
negative.code: 
  handle_cast({{put, Field, Value, Token}, ReplyTo}, S) ->
      S1 = check_write_token(Token, ReplyTo, S,
                            fun (_TokenType) ->
                                do_put(Field, Value, ReplyTo, S)
                            end),
      {noreply, S1, S1#state.timeout};
  