anchor.diff:  -spec is_queue(topic()) -> boolean().
   is_queue(<<"$Q/", _Queue/binary>>) ->
       true;
  +is_queue(<<"$q/", _Queue/binary>>) ->
  +    true;
   is_queue(_) ->
       false.
   
  
positive.code: %% limitations under the License.
  %%--------------------------------------------------------------------
  
  %% @doc MQTT Topic Functions
  -module(emqttd_topic).
  
  -import(lists, [reverse/1]).
  
negative.code: -export([match/2, validate/1, triples/1, words/1, wildcard/1]).
  
  -export([join/1, feed_var/3, is_queue/1, systop/1]).
  
  -ifdef(TEST).
  -compile(export_all).
  -endif.
  
  -type topic() :: binary().
  
  