/**
 * Return true when interval B is fully contained within interval A — every instant of B
 * falls within A.
 *
 * - Uses `Temporal.Instant.compare` for comparison.
 * - Equivalent to 4-argument `intervalContainsUtc(aStart, aEnd, bStart, bEnd)`.
 * - Returns `false` if either interval is invalid (`start > end`).
 * - Returns `false` on invalid input (wrong type, malformed strings, leap seconds).
 *
 * @param aStart ISO 8601 UTC datetime string for the outer interval start
 * @param aEnd ISO 8601 UTC datetime string for the outer interval end
 * @param bStart ISO 8601 UTC datetime string for the inner interval start
 * @param bEnd ISO 8601 UTC datetime string for the inner interval end
 * @returns true if B is fully contained in A, or false on invalid input
 *
 * @example intervalEngulfsUtc("2024-01-01T09:00:00Z", "2024-12-31T17:00:00Z", "2024-06-01T12:00:00Z", "2024-07-01T13:00:00Z") // true
 * @example intervalEngulfsUtc("2024-01-01T09:00:00Z", "2024-12-31T17:00:00Z", "2024-01-01T09:00:00Z", "2024-12-31T17:00:00Z") // true (equal intervals)
 * @example intervalEngulfsUtc("2024-01-01T09:00:00Z", "2024-12-31T17:00:00Z", "2024-01-01T09:00:00Z", "2024-06-30T12:00:00Z") // true
 * @example intervalEngulfsUtc("2024-06-01T12:00:00Z", "2024-07-01T13:00:00Z", "2024-01-01T09:00:00Z", "2024-12-31T17:00:00Z") // false
 * @example intervalEngulfsUtc("invalid", "2024-12-31T17:00:00Z", "2024-06-01T12:00:00Z", "2024-07-01T13:00:00Z") // false
 */
export declare function intervalEngulfsUtc(aStart: string, aEnd: string, bStart: string, bEnd: string): boolean;