This link from the google search has a good explanation:

http://www.mstudiostalk.com/2008/03/...he-navigation/

To a certain extent, Zen Cart already creates relevant body ids; however, they cannot distinguish individual categories, products or ez-pages. Smart Backgrounds in Free Addons can create individual body classes for any of these. By default, it requires an image with a name constructed according to certain rules to activate the class creation. It would be possible to alter its function to always create body class tags. In either case, this can be used to make the article's page identifier. Then you need to alter the menu code to give tags to the menu items.