code: def register_converter(self, converter, conv_type, conv_format=None):
          
          self.flask_plugin.register_converter(converter, conv_type, conv_format)
docs: Register custom path parameter converter
  
          :param BaseConverter converter: Converter.
              Subclass of werkzeug's BaseConverter
          :param str conv_type: Parameter type
          :param str conv_format: Parameter format (optional)