PHP 5 and the integrated Zend Engine 2 have greatly improved PHP's performance and capabilities, but great care has been taken to break as little existing code as possible. So migrating your code from PHP 4 to 5 should be very easy. Most existing PHP 4 code should be ready to run without changes, but you should still know about the few differences and take care to test your code before switching versions in production environments.
Deliver First Class Web Sites: 101 Essential Checklists Want to learn how to make your web sites usable and accessible? Want to ensure that your sites meet current best practice, without spending hours trawling through incomprehensible specifications and recommendations from dozens of different books, research papers, and web sites? Want to make sure that the sites you build are "right the first time," requiring no costly redevelopments?
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