code: func (s *children) insertAt(index int, n *node) {
  	*s = append(*s, nil)
  	if index < len(*s) {
  		copy((*s)[index+1:], (*s)[index:])
  	}
  	(*s)[index] = n
  }
docs: // insertAt inserts a value into the given index, pushing all subsequent values
  // forward.