anchor.diff:      map_property/3,
       year/1,
       to_list/1,
  -    to_labelled_list/1
  +    to_labelled_list/1,
  +    extract_values/1
   ]).
   
   -include_lib("zotonic.hrl").
  
positive.code:     %% Wrap single value in a list for consistency
      [Value].
  
  to_labelled_list(Values) ->
      ListValues = to_list(Values),
      [#{<<"rdfs:label">> => Value} || Value <- ListValues].
  
negative.code: map(Record) ->
      Record.
  
  map_property(Key, [#{<<"value">> := _} | _] = Values, Acc) ->
      E = extract_values(Values),
      %% Flatten Adlib's @lang/value xmltype=grouped structure.
      map_property(Key, E, Acc);
  map_property(Key, #{<<"value">> := Value}, Acc) ->
      %% Flatten Adlib's @lang/value xmltype=grouped structure.
      map_property(Key, Value, Acc);
  