On the Web Developer Juice blog there's a recent post, the first part in a series looking at one of the more handy features of the recent releases of PHP - the magic functions (some which were added in the PHP 5.x series).
There are some reserved function names in PHP class starting with __ ( double underscore ). These are __construct, __destruct, __isset, __unset, __call, __callStatic, __sleep, __wakeup, __get, __set, __toString, __set_state, __invoke and __clone. You cannot use these functions to serve your logical purpose but these are meant to be used for providing magic functionality.
They go through some of the above methods and talk about what role they can play in your code and, for some, a brief bit of code to explain how it works. This first part covers __construct/__destruct and __call/__callStatic.