Returns an aggregation of the maxmimum value n elements within a group. If the group contains fewer than n elements, $maxN returns all elements in the group.
5.2
https://www.mongodb.com/docs/manual/reference/operator/aggregation/maxN/#mongodb-group-grp.-maxN
Returns an aggregation of the maxmimum value n elements within a group. If the group contains fewer than n elements, $maxN returns all elements in the group.