/**
 * Return the latest (maximum) of the given PlainDate values.
 *
 * - Returns null if the array is empty or contains no valid dates.
 * - Validation is performed on each item in the array.
 *
 * @param dates Array of ISO PlainDate strings (e.g. "2024-03-10")
 * @returns The latest date string, or null on invalid input
 *
 * @example maxDate(["2024-03-10", "2024-03-15", "2024-03-12"]) // "2024-03-15"
 * @example maxDate([]) // null
 */
export declare function maxDate(dates: string[]): string | null;