code: protected function saveItems()
      {
          $items = [];
          foreach ($this->items as $name => $item) {
              /* @var $item Item */
              $items[$name] = array_filter(
                  [
                      'type' => $item->type,
                      'description' => $item->description,
                      'ruleName' => $item->ruleName,
                      'data' => $item->data,
                  ]
              );
              if (isset($this->children[$name])) {
                  foreach ($this->children[$name] as $child) {
                      /* @var $child Item */
                      $items[$name]['children'][] = $child->name;
                  }
              }
          }
          $this->saveToFile($items, $this->itemFile);
      }
docs: Saves items data into persistent storage.