/**
 * Parses an HTTP `Retry-After` header into seconds.
 *
 * Accepts either an integer-seconds form (`"30"`) or RFC 7231 HTTP-date
 * (`"Fri, 31 Dec 1999 23:59:59 GMT"`). Returns `null` for unparseable input
 * (including a negative integer-seconds value); an HTTP-date in the past
 * clamps to `0` rather than `null`.
 */
export declare function parseRetryAfter(header: string | null | undefined): number | null;