private function validateBundleMimeVariant(array $bundle)
    {
        if (count($bundle) < 3                          // Too few items in bundle
            || Tokens::MIME_SEPARATOR !== $bundle[1]    // Invalid separator
            || Tokens::isSeparator($bundle[0], true)    // Invalid type
            || Tokens::isSeparator($bundle[2], true)    // Invalid subtype
        ) {
            throw new InvalidVariantException(
                '"' . implode('', $bundle) . '" is not a valid mime type'
            );
        }
    }