Php/docs/class.mongodb-driver-monitoring-subscriber
From Get docs
(mongodb >=1.3.0)
Introduction
Base interface for event subscribers. This is used for type-hinting MongoDB\Driver\Monitoring\addSubscriber() and MongoDB\Driver\Monitoring\removeSubscriber() and should not be implemented directly.
Interface synopsis
MongoDB\Driver\Monitoring\Subscriber {
}
This interface has no methods. Its only purpose is to be the base interface for all event subscribers.