code: func shouldSanitize(r rune) bool {
  	switch {
  	case 'A' <= r && r <= 'Z':
  		fallthrough
  	case 'a' <= r && r <= 'z':
  		fallthrough
  	case '0' <= r && r <= '9':
  		fallthrough
  	case r == '.':
  		fallthrough
  	case r == ':':
  		fallthrough
  	case r == '-':
  		fallthrough
  	case r == '_':
  		return false
  	}
  	return true
  }
docs: // valid librato charactors: A-Za-z0-9.:-_