This post describes how to set up a single web development environment that allows you to test the same files under PHP 4 and PHP 5 at the same time. The Windows versions of Apache and PHP are described, but the same configuration techniques can be applied to other systems.
TACS – Templating and Caching System is a free and lightweight PHP script. It is simple to use and offers easy file includes, variables, code output caching, HTML compression and more. The script is only 10kb in size, works with PHP4 or PHP5, and is easy to incorporate in to any PHP website.
TACS is free to download, use, modify, and distribute.