PHP Zend engine source code Q"s

Hi,

I am studying VM's and their compilers at the moment, and am coming to PHP.
I was wondering if anyone was familar with it and could give me a few
pointers.

Is there a C++ version of the Zend engine, is there or am I imagining
hearing this ? If so it there a browsable CVS/SVN ? If not could you give me
a link to the version control system.

Many thanks in advance,

Aaron