The back button is ubiquitous in Windows 8 ("Metro") apps.
What exactly is its meaning? The Microsoft apps I have seen and the Visual Studio page templates use the button in a chronological manner (back to the page you came from).
But I am currently developing some apps where chronological navigation sometimes does not really make sense (*) and I'm tempted to use the back button for hierarchical navigation instead (back to the page that is above the current one).
Is this a good idea? Does it break user expectations? Does it break the Microsoft UX guidelines or maybe even cause problems during certification?
(*) Think of a game, for example: You go from the start page to a level overview page to a page where you play the selected level. When the level is finished, navigation automatically jumps to the level overview. Now, it would be strange if the back button brought you back to play the level (again?) instead of the start page, or not?