I haven't really had the chance or time to play with PHP 5.3 until recently when Ubuntu 10.04 upgraded my local installations and kind of forced me to dive into it a little. And I'm also probably the last person on the planet to notice, but namespaces in PHP 5.3 allow you to monkey-patch core PHP code. [...] One of the more common applications is stubbing (or mocking) code in unit tests.

He includes a code sample showing how you can use a simple namespace hack to call a function from another namespace named the same as an internal one - in this case strlen.