code: func HandleExtra(msg *config.Message, general *config.Protocol) []config.Message {
  	extra := msg.Extra
  	rmsg := []config.Message{}
  	for _, f := range extra[config.EventFileFailureSize] {
  		fi := f.(config.FileInfo)
  		text := fmt.Sprintf("file %s too big to download (%#v > allowed size: %#v)", fi.Name, fi.Size, general.MediaDownloadSize)
  		rmsg = append(rmsg, config.Message{
  			Text:     text,
  			Username: "<system> ",
  			Channel:  msg.Channel,
  			Account:  msg.Account,
  		})
  	}
  	return rmsg
  }
docs: // HandleExtra manages the supplementary details stored inside a message's 'Extra' field map.