docs: def save_model(self, request, obj, form, change):
          """
          Set the ID of the parent page if passed in via querystring, and
          make sure the new slug propagates to all descendant pages.
          """
          if change and obj._old_slug != obj.slug:
              # _old_slug was set in PageAdminForm.clean_slug().
              new_slug = obj.slug or obj.generate_unique_slug()
              obj.slug = obj._old_slug
              obj.set_slug(new_slug)
  
          # Force parent to be saved to trigger handling of ordering and slugs.
          parent = request.GET.get("parent")
          if parent is not None and not change:
              obj.parent_id = parent
              obj.save()
          super(PageAdmin, self).save_model(request, obj, form, change)