code: func getFormatter(f string) (Formatter, error) {
  	registry.RLock()
  	defer registry.RUnlock()
  
  	formatter := registry.r[f]
  	if formatter == nil {
  		return nil, errors.Reason("unknown formatter: %q", f).Err()
  	}
  	return formatter, nil
  }
docs: // getFormatter returns the Formatter associated with the provided Format.