code: func validateFormatString(v contract.ValueDescriptor) error {
  	// No formatting specified
  	if v.Formatting == "" {
  		return nil
  	}
  
  	match, err := regexp.MatchString(formatSpecifier, v.Formatting)
  
  	if err != nil {
  		LoggingClient.Error("Error checking for format string for value descriptor " + v.Name)
  		return err
  	}
  	if !match {
  		err = fmt.Errorf("format is not a valid printf format")
  		LoggingClient.Error(fmt.Sprintf("Error posting value descriptor. %s", err.Error()))
  		return errors.NewErrValueDescriptorInvalid(v.Name, err)
  	}
  
  	return nil
  }
docs: // Check if the value descriptor matches the format string regular expression