taken from field

Defines the root Node of the scene graph. If a Group is used as the root, the contents of the scene graph will be clipped by the scene's width and height and changes to the scene's size (if user resizes the stage) will not alter the layout of the scene graph. If a resizable node (layout Region or Control) is set as the root, then the root's size will track the scene's size, causing the contents to be relayed out as necessary. Scene doesn't accept null root.