code: func (n *Node) iter(comparator Comparator, start, stop interface{}) iterator {
  	pointer := n.search(comparator, start)
  	pointer--
  	return &sliceIterator{
  		stop:       stop,
  		n:          n,
  		pointer:    pointer,
  		comparator: comparator,
  	}
  }
docs: // iter returns an iterator that will iterate through the provided Morton
  // numbers as they exist in this node.