static public function alnum($value, $message = null, $propertyPath = null)
        {
            try {
                static::regex($value, '(^([a-zA-Z]{1}[a-zA-Z0-9]*)$)');
            } catch(AssertionFailedException $e) {
                $message = $message ?: sprintf(
                    'Value "%s" is not alphanumeric, starting with letters and containing only letters and numbers.',
                    static::stringify($value)
                );

                throw static::createException($value, $message, static::INVALID_ALNUM, $propertyPath);
            }
        }