import type { CustomOptions, CustomValidate } from "../custom/index.ts";
/**
 * Matches a mime type.
 * - group `1`: type
 * - group `2`: subtype
 * - group `3`: suffix
 */
export declare const MIME_REGEX: RegExp;
/**
 * Determines if the input is a mime type.
 *
 * @param input The value to check.
 * @param validate Additional validation to run against the input if it is a mime type. Default is `undefined`.
 * @returns `true` if the input is a mime type, `false` otherwise.
 */
export declare function isMimeType(input: unknown, validate?: CustomValidate<string>): input is string;
export type MimeTypeOptions = Omit<CustomOptions<string>, "typecheck">;
/**
 * Verifies that the input is a mime type, and returns it.
 * If the input is not a mime type, the fallback value is returned.
 *
 * @param input The value to check.
 * @param fallback The value to return if the input is not a mime type. Default is `null`.
 * @returns The mime type value of the input, or the fallback if the input is not a mime type.
 */
export declare function mimeType(input: unknown, fallback: string, options?: MimeTypeOptions): string;
export declare function mimeType(input: unknown, fallback?: string | null | undefined, options?: MimeTypeOptions): string | null;