/**
 * Return a specific date unit extracted from a PlainDate string.
 *
 * - Extracts "year", "month", "day", "week", or "dayOfWeek" from a PlainDate.
 * - Returns zero-padded string for month and day.
 * - Returns "" for invalid input.
 *
 * @param value ISO PlainDate string
 * @param unit unit to extract from the date
 * @param optionsArg optional: weekStartsOn ("monday" | "sunday") for week calculations
 * @returns string representation of the requested unit or "" on invalid input
 *
 * @example parseUnitFromDate("2024-03-15", "year") // "2024"
 * @example parseUnitFromDate("2024-03-15", "month") // "03"
 * @example parseUnitFromDate("2024-03-15", "day") // "15"
 * @example parseUnitFromDate("2024-03-15", "week") // "11"
 * @example parseUnitFromDate("2024-03-15", "dayOfWeek") // "5"
 * @example parseUnitFromDate("invalid", "year") // ""
 * @example parseUnitFromDate("2024-01-01", "week", { weekStartsOn: "sunday" }) // "1"
 */
export declare function parseUnitFromDate(value: string, unit: "year" | "month" | "day" | "week" | "dayOfWeek", optionsArg?: {
    weekStartsOn?: "monday" | "sunday";
}): string;