It seems to be about the "structure" of a packet, meaning bit fields that indicate if the packet is for a single user or multicast? That seems more to me like

It seems to be about the "structure" of a packet, meaning bit fields that indicate if the packet is for a single user or multicast? That seems more to me like a mere protocol convention, exactly the kind of stuff that should be in a standard communication protocol just so everyone agrees on the same fields. How is that a new "invention"?