pub const HOSTNAME_REGEX: &str = r"^([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9-]{0,61}[a-zA-Z0-9])(\\.([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9-]{0,61}[a-zA-Z0-9]))*$";
Regular expression for validating hostnames according to RFC 1123.