code: public function msgType($msgType)
      {
          if (!in_array($msgType, $this->msgTypes, true)) {
              throw new InvalidArgumentException('This message type not exist.');
          }
  
          $this->msgType = $msgType;
  
          return $this;
      }
docs: Set message type.
  
  @param string $msgType
  
  @return MessageBuilder
  
  @throws InvalidArgumentException