Pickupgroup ordering for multiple callgroups

Can anyone confirm the behavior of call pickup when multiple groups are specified in pickupgroup.

I’m hoping that when more than one call is available to be taken via call pickup that there is a predictable behavior to which call is picked up. I would prefer it that the call is picked up from the first callgroup specified in the pickupgroup list but can imagine that it could be the lowest numbered callgroup which is selected. I have not been able to find any documentation which shows what happens in this scenario, so I thought I’d ask here.