SPL in PHP 5.3
Here is a great slideshow that explains what is so important (and so interesting) about the SPL libraries included in PHP 5.3.
And for additional reading, head over to the PHP manual: http://us3.php.net/manual/en/spl.datastructures.php
When I switched QueryPath from an array to an SplObjectStorage object, I noticed tremendous speed improvements. And the 5.3 random access extensions to SPLObjectStorage will continue to speed QueryPath's engine. <!--break-->