code: func (s *Subscription) Dropped() (int, error) {
  	if s == nil {
  		return -1, ErrBadSubscription
  	}
  	s.mu.Lock()
  	defer s.mu.Unlock()
  	if s.conn == nil {
  		return -1, ErrBadSubscription
  	}
  	return s.dropped, nil
  }
docs: // Dropped returns the number of known dropped messages for this subscription.
  // This will correspond to messages dropped by violations of PendingLimits. If
  // the server declares the connection a SlowConsumer, this number may not be
  // valid.