[Android Tablet] Fragment

1. Docs
   
   • http://developer.android.com/guide/topics/fundamentals/fragments.html
   • http://developer.android.com/reference/android/app/Fragment.html
2. What is Fragment
   A Fragment is a piece of an application's user interface or behavior that can be placed in an Activity. It is introduced in Android 3.0.
   
3. Classes
   
   • Fragment
   • DialogFragment
   • ListFragment
   • PreferenceFragment
   • WebViewFragment
     
   • xxx
     
4. xxx