I was researching some libraries in PHP for the interaction of PHP and XMPP, and stumbled across an interesting article on the life cycle of a PHP script - from initialization to shutdown.
It’s an old post (from 2008), but I would imagine the same principles still apply. It’s worth a read if you’re a PHP developer, and want to know a little bit more about the internals of the language you’re working with.
You can view the article at http://abhinavsingh.com/blog/2008/11/how-does-php-echos-a-hello-world-behind-the-scene/.