docs: def link_to_sibling(self, feed, sibling_type, atom_feed):
          """
          Adding previous or next links to the given feed
          self._link_to_sibling(feed, 'previous', atom_feed)
          self._link_to_sibling(feed, 'next', atom_feed)
  
          :param feed: a feed object
          :param sibling_type: 'previous' or 'next'
          :param atom_feed: an atom feed like `feedgen.feed.FeedGenerator`
          """
          sibling = self.atom_feed_manager.get_sibling(feed.id, sibling_type)
          if sibling:
              rel = "prev-archive" if sibling_type == "previous" else "next-archive"
              atom_feed.link(href=self.request.route_url(self.get_atom_feed_url, id=sibling.id),
                             rel=rel)