/** `end` is null while a range is open. */
export interface DateRangeSelection {
    start: Date | null;
    end: Date | null;
}
/**
 * A click opens a range or closes the open one; a single day is the same day twice. No single-day
 * mode, which could strand a user unable to express a range. Bounds come back ordered.
 */
export declare function nextRangeSelection(current: DateRangeSelection, date: Date): DateRangeSelection;
/**
 * `null` unless a range is open, tested exactly as {@link nextRangeSelection} does, so the preview
 * never shows a span the next click would not produce.
 */
export declare function previewEndFor(current: DateRangeSelection, hovered: Date | null): Date | null;