/**
 * Return true if `value` is a valid ISO 8601 duration string.
 *
 * - Uses Temporal.Duration.from to validate.
 * - Accepts date, time, and combined durations, including negative and fractional units.
 *
 * @param value ISO 8601 duration string
 * @returns true if value is a valid ISO 8601 duration string, or false on invalid input
 *
 * @example isValidDuration("P1DT2H30M") // true
 * @example isValidDuration("PT0S") // true
 * @example isValidDuration("-P1D") // true
 * @example isValidDuration("not a duration") // false
 * @example isValidDuration("") // false
 */
export declare function isValidDuration(value: string): boolean;