There are two sides:
https://wiki.openstreetmap.org/wiki/Relation:multipolygon
https://wiki.openstreetmap.org/wiki/Relation:boundary

Both follow the same rules (apart from admin_centre, label and subarea). It is better shown with multipolygons. For the protected_area relations, a single outer ring around the respective area without the inner members is sufficient. (This is like an island, where a forest, a pool, a garden, buildings and so on belong to it and are neither cut out nor added to the relation in any other way.)