/**
 * Return true when interval B is fully contained within interval A — every instant of B
 * falls within A.
 *
 * - Compares numeric Unix epoch values directly.
 * - Equivalent to 4-argument `intervalContainsUnix(aStart, aEnd, bStart, bEnd)`.
 * - Returns `false` if either interval is invalid (`start > end`).
 * - Returns `false` on invalid input (non-numeric types, non-finite values).
 *
 * @param aStart Unix epoch value (seconds or milliseconds) — outer interval start
 * @param aEnd Unix epoch value (seconds or milliseconds) — outer interval end
 * @param bStart Unix epoch value (seconds or milliseconds) — inner interval start
 * @param bEnd Unix epoch value (seconds or milliseconds) — inner interval end
 * @returns true if B is fully contained in A, or false on invalid input
 *
 * @example intervalEngulfsUnix(0, 1700000000, 1500000000, 1600000000) // true
 * @example intervalEngulfsUnix(0, 1700000000, 0, 1700000000) // true (equal intervals)
 * @example intervalEngulfsUnix(0, 1700000000, 0, 1500000000) // true
 * @example intervalEngulfsUnix(1500000000, 1600000000, 0, 1700000000) // false
 * @example intervalEngulfsUnix(NaN, 1700000000, 1500000000, 1600000000) // false
 */
export declare function intervalEngulfsUnix(aStart: number | string, aEnd: number | string, bStart: number | string, bEnd: number | string): boolean;