Usual Android smartphone has 3 buttons bottom of the device.
The left most key is back whose key code is KEYCODE_BACK.
The center key is home whose key code is KEYCODE_HOME.
Looks like D3E doesn't define the key for the back key. Should be 'Back' as UI?
The home key is 'Exit' according to the explanation in the D3E key name list. However, I'm not sure. If not, 'Top' as UI is good name? 'Home' is already defined for Home key on PC keyboard.
Moving to UI Events until we define an extension doc for specific device keys like Android Smartphone.
Perhaps, "HomeScreen" for the KEYCODE_HOME? (I.e., the home button)
Now tracking as: https://github.com/w3c/uievents/issues/12