FYI: I'm going to release us from putting too many classes on screen element to do class control.
For example, if we want to do "swipe-in" transition in the future we do:
<code>app.open('swipe-in');</code>
and it does add "transition-opening ANIMATION_WAY" to the app element. in this case it's __app.transition-opening.swipe-in__

So I hope we have a chance to not overload screen element if possible.