virtual() include path problems

I've been trying to use virtual to include a .shtml file that is outside of my current directory (one level up). I've tried the following: a) virtual("../header.shtml"); b) virtual($_SERVER['DOCUMENT_ROOT'] . "/header.shtml"); c) virtual("/usr/local/psa/home/vhosts/miningstocks.com/httpdocs/header.shtml/"); b & c should be equivalent, because $_SERVER['DOCUMENT_ROOT'] should be the same as /usr/local/psa/home/vhosts/miningstocks.com/httpdocs. With that in mind, both b&c do not work at all. But a does work. Is virtual not supposed to use absolute paths? The documentation on php.net doesn't say either way, but for the include() fuction it says that it should work... Best Regards, Scott Taylor