export declare const MAX_FIXED_DURATION_MS = 8000000000000000;
/** Milliseconds in a fixed ISO-8601 duration, or null for invalid/calendar units. */
export declare function fixedIsoDurationMs(duration: string): number | null;
/**
 * An ISO-8601 period as whole calendar months plus fixed milliseconds, or
 * null. `P1M` is one month, `P1Y` twelve, `P2W` fourteen days. A zero period
 * never advances, so it is refused.
 */
export declare function calendarPeriod(period: string): {
    months: number;
    milliseconds: number;
} | null;
/**
 * `times` periods after `anchor`, in epoch milliseconds. Months are added to
 * the anchor's calendar date in UTC and the day clamps to the month's end, so
 * pieces keep the anchor's day instead of drifting after a short month.
 */
export declare function stepDate(anchor: number, period: {
    months: number;
    milliseconds: number;
}, times: number): number;
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