Extension.php

<?php
/**
 * Validator for the file extension of a file
 *
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Magento\Framework\Validator\File;

class Extension extends \Zend_Validate_File_Extension implements \Magento\Framework\Validator\ValidatorInterface
{
}