/**
 * Checks if a value is set based on its type.
 */
export declare function required(value: unknown): boolean;
/**
 * Checks the value against the given regular expression.
 */
export declare function regex(value: string, expression: RegExp | string): boolean;
/**
 * Checks if the value is a valid email address.
 */
export declare function email(value: string): boolean;
declare const _default: {
    required: typeof required;
    regex: typeof regex;
    email: typeof email;
};
export default _default;