code: public function onViewCreate(ContentfulViewEvent $e)
      {
          $viewMeta                           = $e->getView()->cfMeta;
          $updated                            = $viewMeta['updatedAt'];
          $this->itemIds[$viewMeta['itemId']] = true;
          if ($this->lastModifiedContent === null) {
              $this->lastModifiedContent = $updated;
          } else {
              if ($this->lastModifiedContent < $updated) {
                  $this->lastModifiedContent = $updated;
              }
          }
      }
docs: Collect ViewEvents to build lastModified date.
  
  @param ContentfulViewEvent $e