anchor.diff:  -type replica() :: {timer:timestamp(), nonempty_string()}.
   -record(tagcontent, {id :: binary(),
                        last_modified :: binary(),
  -                     urls :: [binary()]}).
  +                     urls :: [binary()],
  +                     user :: [{binary(), binary()}]}).
   -type tagcontent() :: #tagcontent{}.
   -record(state, {tag, % :: binary(),
                   data :: 'false'  | 'notfound' | 'deleted' | {'error', _}
  
positive.code:     case lists:keysearch(Key, 1, JsonBody) of
          {value, {_, Attrib}} ->
              tag_lookup(JsonBody, Rest, [Attrib|Results]);
          _ -> {error, invalid_object}
      end.
  
  -spec parse_tagcontent(binary()) -> {'error', _} | {'ok', tagcontent()}.
  
negative.code:             {<<"id">>, D#tagcontent.id},
              {<<"version">>, 1},
              {<<"urls">>, D#tagcontent.urls},
              {<<"last-modified">>, D#tagcontent.last_modified},
              {<<"user-data">>, D#tagcontent.user}
          ]})).
  
  -spec tag_lookup(any(), [binary()], [any()]) ->
  