/**
 * Tracks `element`'s viewport-relative bounding rect (via getBoundingClientRect),
 * updating on resize and on scroll of any ancestor scroll container. Only
 * observes while `active` is true, so callers can opt out when not needed
 * (e.g. while a panel using this for positioning is closed).
 */
export declare function useElementRect(element: HTMLElement | null, active: boolean): DOMRect | null;