private function checkType(&$type)
    {
        if ( ! is_string($type)) {
            throw new InvalidTwitterCardException(
                'The Twitter card type must be a string value, [' . gettype($type) . '] was given.'
            );
        }

        $type = strtolower(trim($type));

        if ( ! in_array($type, $this->types())) {
            throw new InvalidTwitterCardException("The Twitter card type [$type] is not supported.");
        }
    }