/**
 * Checks whether two `Date` instances fall on the same calendar day in UTC.
 *
 * Comparison is performed against the UTC components of each date, so a local
 * timezone offset will not affect the result. The time-of-day portion is
 * ignored.
 *
 * @param date1 - The first date to compare.
 * @param date2 - The second date to compare.
 * @returns `true` if both dates share the same UTC year, month, and day;
 *   otherwise `false`.
 *
 * @example
 * ```ts
 * areDatesOfSameDay(
 *   new Date("2026-05-11T01:00:00Z"),
 *   new Date("2026-05-11T23:59:59Z"),
 * ); // true
 *
 * areDatesOfSameDay(
 *   new Date("2026-05-11T00:00:00Z"),
 *   new Date("2026-05-12T00:00:00Z"),
 * ); // false
 * ```
 */
export declare function areDatesOfSameDay(date1: Date, date2: Date): boolean;