code: func SplitList(b []byte) (content, rest []byte, err error) {
  	k, content, rest, err := Split(b)
  	if err != nil {
  		return nil, b, err
  	}
  	if k != List {
  		return nil, b, ErrExpectedList
  	}
  	return content, rest, nil
  }
docs: // SplitList splits b into the content of a list and any remaining
  // bytes after the list.