Good in-depth technical documentation on PHP
<blockquote>
  <p><strong>Possible Duplicate:</strong><br>
  <a href="http://stackoverflow.com/questions/4389738/where-can-i-learn-php-internals-how-they-work">where can i learn php internals, how they work?</a>  </p>
</blockquote>



<p>Are there any good resources for really in depth technical details on php, i.e. the nuts a bolts of how it works.</p>

<p>Most resources don't go beyond actually how to use the language.  Im interested in finding out what goes on below it all (from a high level perspective i.e. i dont want to  sit a read the c code :) )</p>
