Page callback: Displays all the items captured from the particular feed.
\Drupal\aggregator\Plugin\Core\Entity\Feed $feed: The feed for which to display all items.
string The rendered list of items for the feed.
function aggregator_page_source(Feed $feed) {
$feed_source = entity_view($feed, 'default');
// It is safe to include the fid in the query because it's loaded from the
// database by aggregator_feed_load().
$items = aggregator_load_feed_items('source', $feed);
return _aggregator_page_list($items, arg(3), $feed_source);
}