code: func ValidName(val string) bool {
  	if val == "" {
  		return false
  	}
  	for i, r := range val {
  		switch {
  		case 'a' <= r && r <= 'z':
  		case 'A' <= r && r <= 'Z':
  		case r == '_':
  		case i > 0 && '0' <= r && r <= '9':
  		default:
  			return false
  		}
  	}
  	return true
  }
docs: // ValidName returns whether val is a valid name as per the POSIX spec.