Zend Framework requires a PHP 5 interpreter with a web server configured to handle PHP scripts correctly. Some features require additional extensions or web server features; in most cases the framework can be used without them, although performance may suffer or ancillary features may not be fully functional. An example of such a dependency is mod_rewrite in an Apache environment, which can be used to implement "pretty URL's" like "http://www.example.com/user/edit". If mod_rewrite is not enabled, ZF can be configured to support URL's such as "http://www.example.com?controller=user&action=edit". Pretty URL's may be used to shorten URL's for textual representation or search engine optimization (SEO), but they do not directly affect the functionality of the application.