Module ui.widget.container.scrollablecontainer
ScrollableContainer allows scrolling its content (1 widget) within its own dimensions
This scrollable container needs to be known as widget.cropping_widget in the widget using it that is passed to UIManager:show() for UIManager to ensure proper interception of inner widget self-repainting/invert (mostly used when flashing for UI feedback that we want to limit to the cropped area).
If we notice some inner element flashing leaking outside the scrollable area, it's probably some 'show_parent' forwarding missing from the main widget to some of the inner widgets: chase the missing ones and add them.