Requirements

Modifying Constants,
Functions, Classes, and Methods as well as Custom Superglobals works with all releases of PHP
5. No special requirements are necessary.

Sandboxing requires
PHP 5.1.0 or later, or PHP 5.0.0 with a special TSRM patch applied.
Regardless of which version of PHP is in use it must be compiled
with the –enable-maintainer-zts option. See the
README file in the runkit package for additional
information.