code: func (s *RescanChainSource) Subscribe(
  	bestHeight uint32) (*blockntfns.Subscription, error) {
  	return s.blockSubscriptionMgr.NewSubscription(bestHeight)
  }
docs: // Subscribe returns a block subscription that delivers block notifications in
  // order. The bestHeight parameter can be used to signal that a backlog of
  // notifications should be delivered from this height. When providing a height
  // of 0, a backlog will not be delivered.