Comment 3 for bug 36516

The librarian is a part of launchpad. It makes sense to use fmt:url and canonical_url with librarian URLs. The librarian's base URL is available from the launchpad configuration file. This is all the same system, really.

The "cascading" thing ought to be just an optimisation; a convenience. It does allow us to do various kinds of inspection for auto-testing pages and things, so I want to keep it around in most cases. We can choose not to use it for librarian urls, though.

I don't want to use fmt:url for URLs that are truely external to launchpad. I think this would lead to confusion.