The app bar is important because it gives the user easy access your app's commands.
If you use platform button elements, keyboard activation is already supported, but you still need to ensure that buttons can also be activated programmatically (see Making touch events accessible and Verify main app scenarios by using Narrator).
The app bar is also an excellent place to put alternatives for functionality that is otherwise difficult to expose for accessibility. For example, consider the transport controls in Zune Music and Video apps:
Because these controls are used frequently, the app designers decided to expose them in the app bar. Having these controls as buttons in app bar gives the user an easy way to control music and videos with the keyboard and Narrator. This is especially convenient on touch-only devices where finding on-screen transport controls would be a challenge for blind and visually impaired users because the controls disappear after five seconds.
Build date: 11/28/2012
