Ye' old general discussion board. Basically, for everything that isn't covered elsewhere. Come here to shoot the breeze, shoot your mouth off, or whatever suits your fancy. This forum is not for asking programming related questions.
josh posted several post ago a couple links for you to search... maybe you didn't search/read carefully....
here is another link that could help you to find some answers http://devzone.zend.com/node/view/id/1021
but... if happens that you don't look carefully here is some extract from that
"PHP's core is made up of two separate pieces. At the lowest levels you find the Zend Engine (ZE). ZE handles parsing a human-readable script into machine-readable tokens, and then executing those tokens within a process space. ZE also handles memory management, variable scope, and dispatching function calls. The other half of this split personality is the PHP core. PHP handles communication with, and bindings to, the SAPI layer (Server Application Programming Interface, also commonly used to refer to the host environment - Apache, IIS, CLI, CGI, etc). It also provides a unified control layer for safe_mode and open_basedir checks, as well as the streams layer which associates file and network I/O with userspace functions like fopen(), fread(), and fwrite()."
after this paragraph is more to read in the same page related to your questions.
@Jonah Bron with all due respect, guessing isn't likely to give an accurate account of what actually happens. If it were that obvious PHP wouldn't be as unique as it is. What you wrote accurately describes what goes on in a programmer's head when he reads the code, computers think a LOT differently than a programmer though, for example you'll see above it does not parse the code itself, it parses a tokenized (byte code) representation of the code more suitable for machine consumption.
The best bet is to read their unit tests. Unit tests show you exactly whats going on, usually.