In response to a GRSP request (ECE/TRANS/WP29/GRSP/53, para. 45) concerning the configuration of Child Restraint Systems (CRS) combining a base attached to the vehicle by ISOFIX anchorages with a shell installed on the base. This shell could also be used without the base and secured by an adult safety belt. This proposal aims at allowing the type approval of this configuration according to UN Regulation No. 129 in its first phase.