How do you use "archive" property reference to determine XPI install folder?

[email protected] (Jason Bassford) 4 Sep 2002 14:07:06 -0700

Newsgroups	gmane.comp.mozilla.devel.xpinstall
Organization	http://groups.google.com/
Message-ID	<[email protected]>

The value of "archive" holds the full path to the temporary location
of an installing XPI.  So, in my case, if I run "test.xpi" I'd get:

c:\Temp\test.xpi

But how to I get JUST the value of the folder?  (I need to strip out
the filename itself and leave just the folder or, in other words,
"c:\Temp".)