A group that scrolls a child widget using scrollbars and/or mouse or touch dragging.
The widget is sized to its preferred size. If the widget's preferred width or height is less than the size of this scroll pane, it is set to the size of this scroll pane. Scrollbars appear when the widget is larger than the scroll pane.
The scroll pane's preferred size is that of the child widget. At this size, the child widget will not need to scroll, so the scroll pane is typically sized by ignoring the preferred size in one or both directions.
