Proposal to amend UN R17 Supplement 1 to the 12 series of amendments. The Regulation is amended to account for vehicles of category X. Vehicles of category Y are not in the scope of this Regulation. The Regulation is extended to vehicles without driver and manual driving controls. Multiple amendments are made to definitions, test procedures, and technical requirements for seats, anchorages, and head restraints, including changes to measurement planes, test parameters, and displacement specifications across various annexes and paragraphs.