Yes, In this case, you see a dome on a big building. I added a layer=1 to it because it is on top of that building.
When I don't add it, it gives an error for a 'building in a building'.
Normally we only map the footprint; but this was already mapped, so I added this layer.
When mappers work in Ideditor, a building only project, where the roads are already mapped, it happens that buildings need to be mapped over a road. This also gives an error. Often a mapper solve this by adding a layer to that building. This is not the way it should be done, but they cannot move the road a bit aside. In JOSM you can, So validators working in JOSM also.
Validators take care of those issues.
Best regards