code: func (api *PrivateLightServerAPI) SubscribeTotalCapacity(ctx context.Context, onlyUnderrun bool) (*rpc.Subscription, error) {
  	notifier, supported := rpc.NotifierFromContext(ctx)
  	if !supported {
  		return &rpc.Subscription{}, rpc.ErrNotificationsUnsupported
  	}
  	rpcSub := notifier.CreateSubscription()
  	api.server.priorityClientPool.subscribeTotalCapacity(&tcSubscription{notifier, rpcSub, onlyUnderrun})
  	return rpcSub, nil
  }
docs: // SubscribeTotalCapacity subscribes to changed total capacity events.
  // If onlyUnderrun is true then notification is sent only if the total capacity
  // drops under the total capacity of connected priority clients.
  //
  // Note: actually applying decreasing total capacity values is delayed while the
  // notification is sent instantly. This allows lowering the capacity of a priority client
  // or choosing which one to drop before the system drops some of them automatically.