code: public function addAdditionalParentHeaderFields(GetParentHeaderEvent $event)
      {
          $parentModel = $event->getModel();
  
          if (!$parentModel instanceof Model) {
              return;
          }
          $environment = $event->getEnvironment();
          /** @var IMetaModelDataDefinition $definition */
          $definition = $environment->getDataDefinition();
  
          $item          = $parentModel->getItem();
          $metaModel     = $item->getMetaModel();
          $renderSetting = $this->renderSettingFactory->createCollection(
              $metaModel,
              $definition->getMetaModelDefinition()->getActiveRenderSetting()
          );
          $additional    = array();
  
          foreach ($renderSetting->getSettingNames() as $name) {
              $parsed = $item->parseAttribute($name, 'text', $renderSetting);
              $name   = $item->getAttribute($name)->getName();
  
              $additional[$name] = $parsed['text'];
          }
  
          $additional = array_merge(
              $additional,
              $event->getAdditional()
          );
  
          $event->setAdditional($additional);
      }
docs: Add additional parent header fields.
  
  @param GetParentHeaderEvent $event The subscribed event.
  
  @return void