I think the page is this one https://wiki.openstreetmap.org/wiki/One_feature,_one_OSM_element
"An area object with a node object inside, both with the same tags representing the same real-world feature."
An address is a property of the building (or more correctly for Bulgaria: the land the building stands on), so it should be added to the building (the "real-world feature" it belongs to) and only to the building.