import { Temporal } from "@js-temporal/polyfill";
/**
 * Return the start of the specified date `unit` for a given ISO 8601 date string.
 *
 * - Returns "" for invalid inputs.
 *
 * @param value ISO 8601 date string
 * @param unit Temporal.DateUnit to specify the unit for the start
 * @param optionsArg optional: weekStartsOn ("monday" | "sunday")
 * @returns ISO 8601 string representing the start of the specified unit, or "" on invalid input
 *
 * @example startOfDate("2024-02-29", "month") // "2024-02-01"
 * @example startOfDate("invalid-date", "month") // ""
 */
export declare function startOfDate(value: string, unit: Temporal.DateUnit, optionsArg?: {
    weekStartsOn?: "monday" | "sunday";
}): string;