code: protected function getPropertyNames()
      {
          $propertyNames = array('id', 'pid', 'tstamp', 'sorting');
  
          if ($this->getItem()->getMetaModel()->hasVariants()) {
              $propertyNames[] = 'varbase';
              $propertyNames[] = 'vargroup';
          }
  
          return array_merge($propertyNames, array_keys($this->getItem()->getMetaModel()->getAttributes()));
      }
docs: Return the names of all properties stored within this model.
  
  @return string[]