What is the purpose of "modals" and "overlays" in setRoot?

[WJimmyCook]

Hi,

What are the 'modals' and 'overlays' fields used for in setRoot? I thought it might be to show a modal/overlay when the layout is rendered but I can't get that to work.

export interface LayoutRoot {
    /**
     * Set the root
     */
    root: Layout;
    modals?: any;
    overlays?: any;
}