code: public function prepareItem($engine)
      {
          $item = clone $this->item;
          $item->inputOptions['data-engine'] = $engine->primaryKey;
          Html::addCssClass($item->inputOptions, 'storage-field');
  
          return $item;
      }
docs: [[@doctodo method_description:prepareItem]].
  
  @param [[@doctodo param_type:engine]] $engine [[@doctodo param_description:engine]]
  
  @return [[@doctodo return_type:prepareItem]] [[@doctodo return_description:prepareItem]]