I just understand for creating back button in Windows Store App in visual studio 2012 , Microsoft use this Value/Key pairs
<x:String x:Key="BackButtonGlyph"></x:String>
 is a Unicode? If yes how can obtain the list of valid codes for Windows Store Application because I use some of them and It shows me a empty rectangle?
based on This article I create a style.
First, add string dictionary item in StandardStyle.xaml (top of the file)
Then, add following style in another or same xaml file ( style file )