[Zope] HOw Do I Modify A Defined Variable In TAL?

Using TAL and ZPT, I would like to define a global variable myVar, and then later on in the page add 1 to myVar, e.g. myVar = myVar + 1. How can I modify a variable in TAL? I know how to modify a tag using REPLACE, ATTRIBUTES etc., but I want to modify a variable that I have previously defined. __________________________________ Do you Yahoo!? Yahoo! SiteBuilder - Free, easy-to-use web site design software http://sitebuilder.yahoo.com