It is the middle "membership" layer that sits between Heartbeat (a messaging/infrastructure layer) and the new ClusterResourceManager (a resource allocation layer).
Using an enahanced version of the OCF API, it now provides all of the following node information during events published to subscribers:
Node Id (int) : An int who's value is linked to the nodes order in ha.cf... I think.
Node UUID (char*) : A 128-bit guaranteed unique identifier for the node.
Node Born on (int) : The cluster's generation counter at the time this node joined.
Node uname (char*) : The Nodes hostname as determined by uname -n
The last two are used as part of the DesignatedCoordinator's election process.
The order of the list of nodes given is consistent for every member in the partition.