Well I saw an excellent example of it out of Sydney the other day. I left the lounge early but there was already a queue forming as priority pax were just being called. So I sat down and just decided to wait (and also avoid having almost every single passenger walk past my seat). Clear announcement that the priority lane was only for such pax. General boarding by rows would commence in a few minutes. The staff member then checked everyone in the queue to ensure eligibility. When the maybe dozen priority pax were through, they called general boarding through the left lane, back half of the plane only. Announced that priority pax could board any time through the right lane. Then the rest of the plane was called.
I was the last to go through. Fully expected to be in the aerobridge for several minutes but walked probably 70% of the way through and was in my seat 2 minutes later. Obviously an efficient way to board when the rear stairs aren’t an option.