get_route_value is a utility functional available from the tiddlyweb.web.util module which can be used to extract information from an incoming web route. For example the default route for a tiddler inside a bag is:

/bags/{bag_name:segment}/tiddlers/{tiddler_name:segment}

Given a request that matches that route, the bag_name and tiddler_name could be extracted with code such as:

tiddler_title = get_route_value(environ, tiddler_name)
bag_name = get_route_value(bag_name)

This is of most use when creating plugins that add additional routes with dynamic information.