docs: def set_document_type(loader_cls: Type, type_: Type) -> None:
      """Set the type corresponding to the whole document.
  
      Args:
          loader_cls: The loader class to set the document type for.
          type_: The type to loader should process the document into.
      """
      loader_cls.document_type = type_
  
      if not hasattr(loader_cls, '_registered_classes'):
          loader_cls._registered_classes = dict()