From time to time I see questions on Stack Overflow asking “how do I do this thing in XAML that they have done in app X, or how do I hide part of a control template?”. Well, you can attach Visual Studio debugger with the Live Visual Tree view to any XAML app (well, I had success with UWP and WPF apps, not so much with Windows 8 apps so far), even if you don’t have the code and you just installed one from the Store. See this screen cap for details.
WPF Snoop, XAML Spy or even my own WinRT XAML Toolkit have been able to do that for your own apps or any WPF applications for a while, but recently with Visual Studio you can debug any Store app, like MSN News with its funky newspaper layout (it’s all ListViewItem-wrapped Grids in a ListView!) or the all custom XAML-based OneNote with lots of funky-named Office.UI.Xaml.Core controls like a “Silhouette”, “DirectFloatieFlyout” or “FluxPanels”.