I am now able to state this:
-The presented .xml file changes work! With this altered .xml, if you...
-Set the Activity Alpha value to 0 (zero), the activity renders invisible
-Set the Activity Alpha value to 255, the activity renders opaque
-Set the Activity Alpha value between 0 (zero) to 255, the activity renders translucent with a variable transparency
-In either cases, all the other views contained within the ctivity are completly solid and in foreground!.
So I can say that a Widget alike app is already possible to create with 4Android...I only need to test if the "In the back" icons react to click events, when alpha is set to zero