code: func makeInvalidClassnameCharactersUnderscores(name string) string {
  	var sb strings.Builder
  	for _, c := range name {
  		switch {
  		case c >= '0' && c <= '9':
  			sb.WriteRune(c)
  		case c >= 'a' && c <= 'z':
  			sb.WriteRune(c)
  		case c >= 'A' && c <= 'Z':
  			sb.WriteRune(c)
  		default:
  			sb.WriteRune('_')
  		}
  	}
  	return sb.String()
  }
docs: // Replace invalid identifier characters with an underscore