export type WeekdayFormat='narrow'|'short'|'long';export type CalendarMode='single'|'range';
/** Normalize an untyped calendar count to the supported one- or two-month range. */
export declare function normalizeCalendarMonths(value:unknown):1|2;
/** Normalize an untyped weekday format before passing it to `Intl.DateTimeFormat`. */
export declare function normalizeWeekdayFormat(value:unknown):WeekdayFormat;
/** Normalize an untyped picker mode to the single-date default. */
export declare function normalizeCalendarMode(value:unknown):CalendarMode;
/**
* Construct a date formatter while treating a malformed runtime locale as
* the platform default. Attribute values and JavaScript property writes are
* not constrained by TypeScript's declarations, so they must not be allowed
* to turn a calendar render into a `RangeError`.
*/
export declare function dateTimeFormat(locale:unknown,options:Intl.DateTimeFormatOptions):Intl.DateTimeFormat;
/** Local proleptic-Gregorian date construction without Date's legacy 0–99 → 1900 remap. */
export declare function localDate(year:number,month?:number,day?:number):Date;
/** UTC counterpart of {@link localDate}, used for calendar-day arithmetic across DST. */
export declare function utcDate(year:number,month?:number,day?:number):Date;
/** Parse `YYYY-MM-DD` into a local Date, or null if invalid. */
export declare function parseISO(s:string):Date|null;
/** Format a supported Date as local `YYYY-MM-DD`, or an empty string outside years 0000–9999. */
export declare function formatISO(d:Date):string;export declare function isSameDay(a:Date,b:Date):boolean;
/** First day of the month `n` months from `d`. */
export declare function addMonths(d:Date,n:number):Date;
/**
* `d` shifted by `n` months, keeping the same day-of-month unless the target
* month is shorter, in which case the day is clamped to that month's last
* day. Plain `new Date(year, month + n, d.getDate())` construction instead
* overflows a too-large day-of-month into the *following* month (e.g. Jan 31
* + 1 month rolls into March, skipping February entirely) because the Date
* constructor normalizes out-of-range day components rather than clamping
* them.
*/
export declare function addMonthsClampingDay(d:Date,n:number):Date;export declare function clampDate(d:Date,min:Date|null,max:Date|null):Date;
/**
* A 6×7 grid of Dates covering the given month, week-aligned to `firstDayOfWeek`
* (0=Sunday … 6=Saturday). Includes leading/trailing days from adjacent months.
*/
export declare function monthMatrix(year:number,month:number,firstDayOfWeek?:number):Date[][];
/** Localized weekday header labels, ordered from `firstDayOfWeek`. */
export declare function weekdayLabels(firstDayOfWeek?:number,format?:WeekdayFormat,locale?:string):string[];
/** Localized "Month YYYY" title. */
export declare function monthTitle(year:number,month:number,locale?:string):string;
/**
* Resolve a `first-day-of-week` attribute (name or 'auto') to a 0–6 index.
* `'auto'` derives the answer from `locale` via `Intl.Locale`'s week-info
* when the runtime supports it, falling back to Sunday otherwise.
*/
export declare function resolveFirstDayOfWeek(value:string,locale?:string):number;