public Collection<String> getPresenceStates() {
        return presenceStates;
    }
The presence states for which an entity wants to receive notifications. When the owner
is in any of the returned presence states then he is allowed to receive notifications.

@return the presence states for which an entity wants to receive notifications.
        (e.g. available, away, etc.)
xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/NodeSubscription.java