ActivityManager should be able to blur background

[GuyInCorner]

I would use the ActivityManager but I want to be able to blur the background activity beneath it.
Maybe something like:
ActivityManager { showBackground: true; effects.blur: 2; }

[GuyInCorner]

After more experimentation I would say that the option to show the background (previous activity) and/or blur it should be at the option of the new activity being pushed onto the stack. Some activities would want this and some wouldn't.