code: def _get_parent_classes_transparent(cls, slot, page, instance=None):
          
          parent_classes = super(CascadePluginBase, cls).get_parent_classes(slot, page, instance)
          if parent_classes is None:
              if cls.get_require_parent(slot, page) is False:
                  return
              parent_classes = []
  
          # add all plugins marked as 'transparent', since they all are potential parents
          parent_classes = set(parent_classes)
          parent_classes.update(TransparentContainer.get_plugins())
          return list(parent_classes)
docs: Return all parent classes including those marked as "transparent".