import { FetchParams } from './types';
export declare function decodeXmlEntities(text: string): string;
export declare function retrieveVideoId(videoId: string): string;
/**
 * Validate that a language code matches a BCP 47-like pattern.
 * @throws {@link YoutubeTranscriptInvalidLangError} if the language code is invalid.
 */
export declare function validateLang(lang: string): void;
export declare function defaultFetch(params: FetchParams): Promise<Response>;
/** Returns true if the HTTP status code is retryable (429 or 5xx). */
export declare function isRetryableStatus(status: number): boolean;
/**
 * Wrap a fetch call with retry logic using exponential backoff.
 *
 * Retries on 429 (Too Many Requests) and 5xx (Server Errors).
 * Client errors (4xx other than 429) are returned immediately.
 *
 * @param fetchFn - Function that performs the fetch call.
 * @param retries - Maximum number of retry attempts (0 = no retries).
 * @param retryDelay - Base delay in milliseconds for exponential backoff.
 * @param signal - Optional AbortSignal to cancel the operation.
 * @returns The fetch Response.
 */
export declare function fetchWithRetry(fetchFn: () => Promise<Response>, retries: number, retryDelay: number, signal?: AbortSignal): Promise<Response>;