code: def as_bookmark_class(xso_class):
      
  
      if not issubclass(xso_class, Bookmark):
          raise TypeError(
              "Classes registered as bookmark types must be Bookmark subclasses"
          )
  
      Storage.register_child(
          Storage.bookmarks,
          xso_class
      )
  
      return xso_class
docs: Decorator to register `xso_class` as a custom bookmark class.
  
      This is necessary to store and retrieve such bookmarks.
      The registered class must be a subclass of the abstract base class
      :class:`Bookmark`.
  
      :raises TypeError: if `xso_class` is not a subclass of :class:`Bookmark`.