code: func newFilter(backend Backend, addresses []common.Address, topics [][]common.Hash) *Filter {
  	return &Filter{
  		backend:   backend,
  		addresses: addresses,
  		topics:    topics,
  		db:        backend.ChainDb(),
  	}
  }
docs: // newFilter creates a generic filter that can either filter based on a block hash,
  // or based on range queries. The search criteria needs to be explicitly set.