An online book about PHP internals, written by three core developers.
phpinternalsbook.com
#php internals reading
2 tools curated in this category — including PHP Internals Book, PHP RFCs
Find on mySelectas all sites and tools related to php internals reading. This selection of 2 resources is reviewed and maintained by the community. The most popular include PHP Internals Book, PHP RFCs. Each tool comes with a review, tags, comparisons and alternatives to help you make the best choice.
The home of PHP RFCs (Request for Comments).
wiki.php.net