def app_template_filter(
        self, name: str | None = None
    ) -> t.Callable[[T_template_filter], T_template_filter]:
        """Register a template filter, available in any template rendered by the
        application. Equivalent to :meth:`.Flask.template_filter`.

        :param name: the optional name of the filter, otherwise the
                     function name will be used.
        """

        def decorator(f: T_template_filter) -> T_template_filter:
            self.add_app_template_filter(f, name=name)
            return f

        return decorator
Register a template filter, available in any template rendered by the
        application. Equivalent to :meth:`.Flask.template_filter`.

        :param name: the optional name of the filter, otherwise the
                     function name will be used.
        
src/flask/sansio/blueprints.py