export type DateBoundaryUnit = "second" | "minute" | "hour" | "day" | "week" | "month" | "quarter" | "year";
/**
 * Returns a new Date set to the start of the given unit.
 * Week start is Sunday (day 0).
 *
 * @param {Date} date - Base date
 * @param {DateBoundaryUnit} unit - Boundary unit
 * @returns {Date} A new Date at the start of the specified unit
 * @example
 * startOf(new Date("2025-04-15T10:30:00"), "day"); // 2025-04-15T00:00:00
 * startOf(new Date("2025-04-15"), "month"); // 2025-04-01T00:00:00
 */
export declare const startOf: (date: Date, unit: DateBoundaryUnit) => Date;