"Unsupported Updates (raring-backports)"... Packages may contain new features, may introduce new interfaces, and have not been sufficiently tested to be included in the 'proposed' repository.
This implies to me that packages firstly land in the "backports" repository. If they are then sufficiently tested, then they will move to the "proposed" repository. Hence, "proposed" would appear to be more tested than "backports". Is this true, am I reading the official website wrong, or is this misinformation?