/**
 * Return true when `value` falls on a weekend day for `locale`.
 *
 * - Uses `Intl.Locale.prototype.weekInfo` to resolve which ISO weekday
 *   numbers count as "weekend" for the locale (e.g. en-US: Sat/Sun,
 *   he-IL/ar-SA: Fri/Sat).
 * - Falls back to Saturday/Sunday if the runtime's `weekInfo` data doesn't
 *   resolve a weekend for the locale.
 * - Returns false if `value` or `locale` is invalid.
 *
 * @param value ISO PlainDate string
 * @param locale BCP 47 locale tag (e.g. "en-US", "he-IL")
 * @returns true if `value` is a weekend day in `locale`, false on invalid input
 *
 * @example isWeekend("2024-02-03", "en-US") // true (Saturday, en-US weekend is Sat/Sun)
 * @example isWeekend("2024-02-02", "he-IL") // true (Friday, he-IL weekend is Fri/Sat)
 * @example isWeekend("2024-02-04", "he-IL") // false (Sunday, not part of he-IL's weekend)
 * @example isWeekend("invalid", "en-US") // false
 * @example isWeekend("2024-02-03", "not-a-locale") // false
 */
export declare function isWeekend(value: string, locale: string): boolean;