public int getDepth() {
        return depth;
    }
Returns 1 when the subscriber wants to receive notifications only from first-level
children of the collection. A value of 0 means that the subscriber wants to receive
notifications from all descendents.

@return 1 when the subscriber wants to receive notifications only from first-level
        children of the collection or 0 when notififying only from all descendents.
xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/NodeSubscription.java