public boolean isMultipleSubscriptionsEnabled() {
        return getService().isMultipleSubscriptionsEnabled();
    }
Returns true if a user may have more than one subscription with the node. When
multiple subscriptions is enabled each subscription request, event notification and
unsubscription request should include a {@code subid} attribute. By default multiple
subscriptions is enabled.

@return true if a user may have more than one subscription with the node.
xmppserver/src/main/java/org/jivesoftware/openfire/pubsub/Node.java