code: func splitTokens(tokens []string, sep string) (s splitted, err error) {
  	index := index(tokens, sep)
  	if index == -1 {
  		return s, fmt.Errorf("'%s' not found in ['%s']", sep, strings.Join(tokens, "','"))
  	}
  	return splitted{
  		Left:  tokens[:index],
  		Right: tokens[index+1:],
  	}, nil
  }
docs: // Split a list of tokens by a token into a splitted struct holding the tokens
  // before and after the token to be split by.