In the phpBB 3.1 User Pruning update, the Group drop-down help says "Selects all members of the group for pruning". I think that could mislead people into thinking that everybody in the group would be pruned (perhaps overriding the ANDing of the other fields). Presuming that's not the case, I would say "Only members of the group will be candidates for pruning", which implies that the other criteria can filter them even more.