/**
 * Validates a field against an email pattern.
 * Based on "pattern", so in form one must use `hasError('pattern')` to get validation results.
 *
 * @param msg A custom message. If not provided "The field ffff must contain a valid e-mail address."
 *             will be generated, while ffff is the property name.
 *
 */
export declare function Email(msg?: string): (target: object, property: string | symbol) => void;