docs: def send_file_from_directory(filename, directory, app=None):
      """Helper to add static rules, like in `abilian.app`.app.
  
      Example use::
  
         app.add_url_rule(
            app.static_url_path + '/abilian/<path:filename>',
            endpoint='abilian_static',
            view_func=partial(send_file_from_directory,
                              directory='/path/to/static/files/dir'))
      """
      if app is None:
          app = current_app
      cache_timeout = app.get_send_file_max_age(filename)
      return send_from_directory(directory, filename, cache_timeout=cache_timeout)