code: func (c *ChainIndexer) Start(chain ChainIndexerChain) {
  	events := make(chan ChainHeadEvent, 10)
  	sub := chain.SubscribeChainHeadEvent(events)
  
  	go c.eventLoop(chain.CurrentHeader(), events, sub)
  }
docs: // Start creates a goroutine to feed chain head events into the indexer for
  // cascading background processing. Children do not need to be started, they
  // are notified about new events by their parents.