Build polished collection and list apps using XAML

There were some questions about fallback among regional variants. E.g., the app has strings for en-US and de-DE with de-DE as the ultimate fallback; but the user's preference is for en-AU. In this case, the en-US strings will be used. The system will look at the user's preference and infer a fallback chain that allows for regional variants. So, in the above example, it will assume a fallback chain as follows:
Note that, as explained by Tim Heuer, you don't have to declare the resources using a specific regional variant language tag. You can, instead, use a region-neutral tag like "en". And you can use any combination of specific-regional variants as well as a region-neutral variant.
How does the Uid property interact with primatives?.
All of the samples define the application title as a String resource in either the page or the App. There's a Uid property available on it, but I'm if I try to set it, I get a runtime exception for a missing resource.
Is there going to be some design time indication what is and isn't supported to avoid runtime issues later?
@MikeKenyon -- Hi mike can you ask this question over on the forums (dev.windows.com)? I know it is annoying to ask, but I want others to have the answer as well.
UID support on primitives isn't supported, but this is something that I'll log a bug on to investigate.