import { Temporal } from "@js-temporal/polyfill";
import type { FractionalDigit } from "../../types/index.js";
type StartOfTimeUnit = Temporal.TimeUnit | "day";
/**
 * Return the start of the specified time `unit` for a given ISO 8601 time string.
 *
 * - Returns "" for invalid inputs.
 *
 * @param value ISO 8601 time string
 * @param unit StartOfTimeUnit to specify the unit for the start
 * @param optionsArg optional: fractionalSecondDigits (number)
 * @returns ISO 8601 string representing the start of the specified unit, or "" on invalid input
 *
 * @example startOfTime("12:34:56", "hour") // "12:00:00"
 * @example startOfTime("invalid", "hour") // ""
 */
export declare function startOfTime(value: string, unit: StartOfTimeUnit, optionsArg?: {
    fractionalSecondDigits?: FractionalDigit;
}): string;
export {};