/**
 * 4, 7, 8 heading are allowed since 2018
 * news: https://skypost.ulifestyle.com.hk/article/2006268/
 * */
export declare function is_hk_mobile_phone_prefix(s: string): boolean;
/**
 * with/without +852 prefix
 * */
export declare function is_hk_mobile_phone(x: number | string): boolean;
/**
 * very forgiving
 *
 * @return +852xxxxyyyy if valid
 *         empty string if not valid
 * */
export declare function to_full_hk_mobile_phone(s: string | number): string;
export declare function is_email(s: string): boolean;