/**
 * Checks if the argument is a real boolean.
 * @param value The value being checked.
 * @returns True if the argument is an instance of Boolean.
 */
export declare function isBoolean(value: any): boolean;
/**
 * Throws an `IsError` if the value does not pass the `isBoolean` check.
 * @param value The value being checked.
 * @param field The name of the field being checked.
 * @param code The application / module code assigned to this error.
 * @throws IsError if the value is not a Boolean instance.
 * @returns false if an {@link IsError} is not thrown
 */
export declare function isBooleanError(value: any, field: string, code?: string): boolean;