anchor.diff:  map(Record) ->
       Record.
   
  -map_property(Key, [#{<<"value">> := Value}], Acc) ->
  +map_property(Key, [#{<<"value">> := _} | _] = Values, Acc) ->
  +    E = extract_values(Values),
       %% Flatten Adlib's @lang/value xmltype=grouped structure.
  -    map_property(Key, Value, Acc);
  +    map_property(Key, E, Acc);
   map_property(Key, #{<<"value">> := Value}, Acc) ->
       %% Flatten Adlib's @lang/value xmltype=grouped structure.
       map_property(Key, Value, Acc);
  
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_property/3,
      year/1,
      to_list/1,
      to_labelled_list/1,
      extract_values/1
  ]).
  
  -include_lib("zotonic.hrl").
  