/**
 * Return true if `value1` and `value2` form a valid UTC range — both parseable as
 * ISO UTC datetime strings and the instant at `value1` is <= the instant at `value2`.
 *
 * - Both inputs must be ISO 8601 UTC datetime strings (e.g. `"2024-01-01T10:00:00Z"`).
 * - Equal `value1 === value2` is valid when `options.allowEqual` is true.
 * - Leap-second strings return `false`.
 * - Invalid input or malformed strings return `false`.
 *
 * @param value1 first ISO UTC datetime string
 * @param value2 second ISO UTC datetime string
 * @param options optional allowEqual flag
 * @returns boolean indicating whether the UTC range is valid
 *
 * @example isValidUtcRange({ value1: "2024-01-01T10:00:00Z", value2: "2024-12-31T23:59:59Z" }) // true
 * @example isValidUtcRange({ value1: "2024-12-31T23:59:59Z", value2: "2024-01-01T10:00:00Z" }) // false
 * @example isValidUtcRange({ value1: "2024-01-01T10:00:00Z", value2: "2024-01-01T10:00:00Z", options: { allowEqual: true } }) // true
 */
export declare function isValidUtcRange({ value1, value2, options, }: {
    value1: string;
    value2: string;
    options?: {
        allowEqual?: boolean;
    };
}): boolean;