code: protected function _pushMessage($message, $type = 'error', array $interpolateParams = [])
      {
          $this->_messages[] = [
              'message'   => vsprintf($message, $interpolateParams),
              'type'      => $type,
          ];
  
          return $this;
      }
docs: Push a message, allowing it to be shown to clients.
  
  @param string $message
  @param string $type Type of the message (info, warning, error, etc)
  @param array $interpolateParams Params to interpolate within $message
  @return self