code: func sanitizeName(name string) string {
  	output := strings.ToLower(illegalChars.ReplaceAllString(name, "_"))
  
  	if legalLabel.MatchString(output) {
  		return output
  	}
  	// Prefix name with _ if it begins with a number
  	return "_" + output
  }
docs: // sanitizeName returns a metric or label name which is safe for use
  // in prometheus output