Slots in the rear parcel shelf, what are they really for? Seatbelts?

Any one got photos of how the top anchor attaches or is welded to parcel shelf?
Mine are already installed so no photos but there are reinforcement plates below the package tray which are held in with screws . the seatbelt has a loop sewn on the end which slides thru the plastic trim bezel and tray...a steel dogbone about 4"long then slides thru the loop then you pull the belt up and the dogbone snaps into the legs of the plastic bezel.