I'm not really going to go too much in detail about the Extending PHP session I was at yesterday, which was presented by Marcus Boerger and Sara Golemon. It was a pretty technical look at how to write extensions for PHP. Any discussion on extending php, though, has to explain a fair amount of php's internal workings, and that's really why I was there. It was a bit informative, although they had planned for a six hour presentation, and there was only three hours, so they didn't get through the entirety of their material. A fair amount of the material they covered appears to have come from this
PHP Extension Writing Tutorials page on zend's website, so it looks like I'll have some further reading material for later.