anchor.diff:              {<<"version">>, 1},
               {<<"urls">>, D#tagcontent.urls},
               {<<"last-modified">>, D#tagcontent.last_modified},
  -            {<<"user-data">>, D#tagcontent.user}
  +            {<<"user-data">>, {struct, D#tagcontent.user}}
           ]})).
   
   -spec tag_lookup(any(), [binary()], [any()]) ->
  
positive.code:         false ->
              case Key of
                  <<"user-data">> ->
                      tag_lookup(JsonBody, Rest, [[] | Results]);
                  _ ->
                      {error, not_found}
              end
  
negative.code:             case tag_lookup(Body,
                              [<<"id">>, <<"urls">>, <<"last-modified">>, <<"user-data">>],
                              []) of
                  {ok, [Id, Urls, LastModified, {struct, UserData}]} ->
                      {ok, #tagcontent{id = Id,
                                       last_modified = LastModified,
                                       urls = Urls,
  