When Sarge becomes stable - upgrading?

["John Fleming" <wa9als@starband.net>]

Consider the case of someone running testing when it becomes the stable
release.  At that point, can they change apt sources to stable and security
and continue updating/upgrading?  Or do they have to stay with the testing
sources?

I know about dist-upgrading to a less stable release, but I'd like more info
about what happens when testing becomes the stable release.  I know one can
stay with testing, but can they switch to stable sources at that point?
Thanks - John