/**
 * Return the overlapping span of two datetime intervals, or null when they do not overlap.
 *
 * - Uses `Temporal.PlainDateTime.compare` for comparison.
 * - Adjacent intervals (e.g. `aEnd === bStart`) share one instant and DO overlap.
 * - Returns `null` if either interval is invalid (`start > end`).
 * - Returns `null` on invalid input (wrong type, malformed strings).
 *
 * @param aStart ISO 8601 datetime string for the first interval start
 * @param aEnd ISO 8601 datetime string for the first interval end
 * @param bStart ISO 8601 datetime string for the second interval start
 * @param bEnd ISO 8601 datetime string for the second interval end
 * @returns `{ start, end }` with the overlapping span, or null on invalid input / no overlap
 *
 * @example intervalIntersectionDateTime("2024-01-01T10:00:00", "2024-06-30T23:59:59", "2024-04-01T00:00:00", "2024-12-31T23:59:59") // { start: "2024-04-01T00:00:00", end: "2024-06-30T23:59:59" }
 * @example intervalIntersectionDateTime("2024-01-01T10:00:00", "2024-06-30T23:59:59", "2024-07-01T00:00:00", "2024-12-31T23:59:59") // null
 * @example intervalIntersectionDateTime("2024-01-01T10:00:00", "2024-06-30T23:59:59", "2024-07-02T00:00:00", "2024-12-31T23:59:59") // null
 * @example intervalIntersectionDateTime("invalid", "2024-06-30T23:59:59", "2024-04-01T00:00:00", "2024-12-31T23:59:59") // null
 */
export declare function intervalIntersectionDateTime(aStart: string, aEnd: string, bStart: string, bEnd: string): {
    start: string;
    end: string;
} | null;