12.2. Catalog variables
Interchange provides a very useful feature that has not been discussed yet called catalog variables. It provides a way for you to set a variable to a certain value in the catalog.cfg file and use it anywhere in your catalog pages. The Variable directive allows an Interchange catalog variable to be created with the name coming from the first parameter and the value from the rest of the line, like this:
Variable SOMENAME whatever value you want
To access that variable in your pages, type the token __SOMENAME__. Notice that there are two underscore characters before the variable name and two after it, and that in place of the word SOMENAME you would put the actual name of the variable. The first thing Interchange does on a page is to replace the token with the variable's value. The value can also include Interchange tags to be parsed.