RhythmDBExtraData* rhythmdb_extradata_new (void);

void rhythmdb_extradata_add (RhythmDBExtraData *extra, RhythmDBPropType prop, GValue *value);
void rhythmdb_extradata_remove (RhythmDBExtraData *extra, RhythmDBPropType prop, GValue *value);
gboolean rhythmdb_extradata_contains (RhythmDBExtraData *extra, RhythmDBPropType prop, GValue *value);