Two steps to embedding an iframe in every node of a Drupal 8 site
Sometimes you have the necessity to put in a fixed position of every article of your site a block of content, in my case one or more adverts, but Drupal 8 and its new theming system doesn't help you much. So I'll try to show you my first rough solution via jQuery and iframe, hoping to obtain some idea to improve it or another method more efficient, maybe through only Twig.