How does PHP work - literature

Question

I'm interested in literature (articles on internet, in magazines, books, podcasts - I don't really mind anything) that describes how PHP works internally, about its gotchas and perhaps some advanced functions. Is there anything like this out there? I tried to search on Google, but majority of articles were about starting with PHP and its basic functions.

Any input is really welcome as I'm trying to understand the language internally - I'm tired of my mindless typing of code without understanding its essence.

Answer 1

There's a section in the PHP Manual entitled PHP at the Core: A Hackers' Guide to the Zend Engine

http://www.php.net/manual/en/internals2.php

Answer 2

The Extending and Embedding PHP book written by Sara Golemon is an interesting read, when it comes to the internals of PHP and its extensions system.

It's not really speaky about PHP's internals per se, but, as extensions are close to those internals, the informations given in that book are close internals.
(Humph, even I had to re-read my sentence to understand it...)