/**
 * Moves focus into an open DatePicker popup in order: selected date, else today,
 * else cell holding grid's roving tab stop, else first tabbable, else panel itself.
 *
 * @param content the popup panel, already mounted and positioned
 * @param selectedISO the anchor date as `YYYY-MM-DD`, or `null` when nothing is selected
 * @returns the element that took focus, or `null` when nothing could
 */
export declare function focusDatePickerContent(content: HTMLElement, selectedISO: string | null): HTMLElement | null;