export function formatDate(value: Date, options: Intl.DateTimeFormatOptions): string;
/**
 * Number of cells in the day grid: six weeks, enough to show any month in full from the Sunday on
 * or before its first day.
 */
export const DAY_GRID_SIZE: 42;
/**
 * List of month names for the month selector. We use a fixed date to avoid issues with daylight
 * saving time.
 * @type {string[]}
 */
export const MONTH_NAMES: string[];
export function getFirstDayOfMonth(date: Date): Date;
export function addMonths(firstDay: Date, delta: number): Date;
export function getCalendarDays(firstDay: Date): Date[];
export function toDateString(date: Date): string;
export function isSameDay(a: Date, b: Date): boolean;