import type { CustomOptions } from "../custom/index.ts";
/**
 * Determines if the input is a boolean.
 *
 * @param input The value to check.
 * @returns `true` if the input is a boolean, `false` otherwise.
 */
export declare function isBoolean(input: unknown): input is boolean;
export type BooleanOptions = Omit<CustomOptions<boolean>, "typecheck" | "transform" | "validate">;
/**
 * Verifies that the input is a boolean, and returns it.
 * If the input is not a boolean, the fallback value is returned.
 *
 * @param input The value to check.
 * @param fallback The value to return if the input is not a boolean. Default is `false`.
 * @returns The boolean value of the input, or the fallback if the input is not a boolean.
 */
export declare function boolean(input: unknown, fallback: boolean, options?: BooleanOptions): boolean;
export declare function boolean(input: unknown, fallback?: boolean | null | undefined, options?: BooleanOptions): boolean | null;
export interface ToBooleanOptions {
    true?: (string | number | bigint)[];
    false?: (string | number | bigint)[];
}
/**
 * Converts the input to a boolean.
 *
 * @param input The value to convert.
 * @param options The options to use when converting the input to a boolean.
 * @returns The boolean representation of the input, or `null` if the input is not a boolean.
 */
export declare function toBoolean(input: unknown, options?: ToBooleanOptions): boolean | null;