Part of canonical.launchpad.webapp View In Hierarchy
It is a class advisor in its two argument form or as a descriptor. It says what name is mapped to where.
It is an object returned from a traversal method in its one argument form. It says that the result of such traversal is a redirect.
You can use the keyword argument 'status' to change the status code from the default of 303 (assuming http/1.1).