code: func (rtm *RTM) NewTypingMessage(channelID string) *OutgoingMessage {
  	id := rtm.idGen.Next()
  	return &OutgoingMessage{
  		ID:      id,
  		Type:    "typing",
  		Channel: channelID,
  	}
  }
docs: // NewTypingMessage prepares an OutgoingMessage that the user can
  // use to send as a typing indicator. Use this function to properly set the
  // messageID.