code: func newInsertIterator(chain types.Blocks, results <-chan error, validator Validator) *insertIterator {
  	return &insertIterator{
  		chain:     chain,
  		results:   results,
  		errors:    make([]error, 0, len(chain)),
  		index:     -1,
  		validator: validator,
  	}
  }
docs: // newInsertIterator creates a new iterator based on the given blocks, which are
  // assumed to be a contiguous chain.