docs: def clean_slug(self):
          """
          Save the old slug to be used later in PageAdmin.save_model()
          to make the slug change propagate down the page tree, and clean
          leading and trailing slashes which are added on elsewhere.
          """
          self.instance._old_slug = self.instance.slug
          new_slug = self.cleaned_data['slug']
          if not isinstance(self.instance, Link) and new_slug != "/":
              new_slug = clean_slashes(self.cleaned_data['slug'])
          return new_slug