/**
 * Excel serial date conversion (1900 / 1904 systems).
 *
 * Numbers remain the on-wire cell values; these helpers only map public
 * `Cell.dateTime` to/from serials. The 1900 system keeps Excel’s fictitious
 * 1900-02-29 (serial 60) for Lotus 1-2-3 compatibility.
 *
 * Citations: ECMA-376-1 workbookPr/@date1904; engineering-reference-pack
 * cells-and-values (1900 leap-day quirk).
 */
/** Default number format applied when authoring via `Cell.dateTime`. */
export declare const DEFAULT_DATE_TIME_FORMAT = "yyyy-mm-dd hh:mm";
/**
 * Convert a local civil `Date` to an Excel serial using the workbook date system.
 *
 * Local Y/M/D/h/m/s/ms components are used so round-trips match `Date` getters
 * in the host timezone (public-API contract for `Cell.dateTime`).
 */
export declare function dateToExcelSerial(date: Date, date1904: boolean): number;
/**
 * Convert an Excel serial to a local civil `Date` (new instance every call).
 *
 * Serial 60 in the 1900 system is the non-existent 1900-02-29; JS has no such
 * civil day, so it surfaces as 1900-03-01 local (same roll Excel UIs often show
 * when materializing that serial outside the spreadsheet grid).
 */
export declare function excelSerialToDate(serial: number, date1904: boolean): Date;