/**
 * Return true when intervals `[aStart, aEnd]` and `[bStart, bEnd]` share at least one instant.
 *
 * - Uses `Temporal.PlainDate.compare` for comparison.
 * - Adjacent intervals (e.g. `aEnd === bStart`) do NOT overlap — returns `false`.
 * - Returns `false` if either interval is invalid (`start > end`).
 * - Returns `false` on invalid input (wrong type, malformed strings).
 * - Accepts GMT calendar-annotated PlainDate strings — E5 (issue #78). Ordering is
 *   calendar-independent, so arguments may carry different or no calendar tags (D4).
 *
 * @param aStart ISO 8601 date string for the first interval start, optionally calendar-annotated
 * @param aEnd ISO 8601 date string for the first interval end, optionally calendar-annotated
 * @param bStart ISO 8601 date string for the second interval start, optionally calendar-annotated
 * @param bEnd ISO 8601 date string for the second interval end, optionally calendar-annotated
 * @returns true if intervals overlap, or false on invalid input
 *
 * @example intervalsOverlapDate("2024-01-01", "2024-06-30", "2024-04-01", "2024-12-31") // true
 * @example intervalsOverlapDate("2024-01-01", "2024-06-30", "2024-07-01", "2024-12-31") // false (adjacent)
 * @example intervalsOverlapDate("2024-01-01", "2024-06-30", "2024-07-02", "2024-12-31") // false (disjoint)
 * @example intervalsOverlapDate("2024-01-01", "2024-06-30", "2024-02-01", "2024-03-01") // true (partial)
 * @example intervalsOverlapDate("invalid", "2024-06-30", "2024-04-01", "2024-12-31") // false
 */
export declare function intervalsOverlapDate(aStart: string, aEnd: string, bStart: string, bEnd: string): boolean;