This standard applies to: (a) Vehicles of categories M1 and N1 with regard to the strength of seats and their anchorages and with regard to their head restraints; (b) Vehicles of categories M2 and M31 with regard to seats not covered by Regulation No. 80, in respect of the strength of seats and their anchorages, and in respect of their head restraints; (c) Vehicles of category M1 with regard to the design of the rear parts of seat backs and the design of devices intended to protect the occupants from the danger resulting from the displacement of luggage in a frontal impact. It does not apply to vehicles with regard to side-facing or rearward-facing seats, or to any head restraint fitted to these seats.