The MPE spec 1.0 includes two zones. The Lower Zone uses channel 1 as a master for messages that apply to all channels in the zone. The Upper Zone uses channel 16 as a master. Per section 2.1.1 the member channels are 2 up for the Lower Zone and 15 down for the Upper Zone. So basically this seems to be a codification of what controllers usually call split.
Does any software support this yet? I haven’t seen a Zone property in the MPE soft synths I’ve played around with, though it might be hidden if it doesn’t detect zones in use on the controller.
There’s a link on this page to download the spec (requires free membership):