/**
 * Focuses `target` once its popover can take focus, then calls `done`.
 * TxBaseAnchor keeps the panel at `visibility: hidden` until its open motion
 * starts, a few frames after the content mounts (later on the first open,
 * which loads GSAP), and focusing a hidden element does nothing.
 */
export declare function focusWhenShown(target: () => HTMLElement | null | undefined, done?: () => void, timeout?: number): void;