code: func parseTag(s string) (prefix, tag string, err error) {
  	splitString := strings.Split(s, ":")
  	if len(splitString) == 1 {
  		prefix = splitString[0]
  	} else if len(splitString) == 2 {
  		prefix, tag = splitString[0], splitString[1]
  	} else {
  		// Unlikely edge case but it doesn't hurt to test for it.
  		return "", "", fmt.Errorf("Path should not contain more than one colon: %q", s)
  	}
  
  	if strings.HasSuffix(prefix, "/") {
  		return "", "", fmt.Errorf(`Image name must not have a trailing "/": %s`, prefix)
  	}
  
  	return prefix, tag, nil
  }
docs: // parseTag splits the Repository tag from the prefix.