Groups

A group is a collection of objects and is a sub-unit of a track (Section 2.4). Groups SHOULD be indendepently useful, so objects within a group SHOULD NOT depend on objects in other groups. A group provides a join point for subscriptions, so a subscriber that does not want to receive the entire track can opt to receive only the latest group(s). The publisher then selectively transmits objects based on their group membership. Groups can contain any number of objects.

Within a track, the original publisher SHOULD produce Group IDs which increase with time. Subscribers to tracks which do not follow this requirement SHOULD NOT use range filters which span multiple groups in FETCH or SUBSCRIBE. SUBSCRIBE and FETCH delivery use Group Order, so a FETCH cannot deliver Groups out of order and a subscription could have unexpected delivery order if Group IDs do not increase with time.