2. About Variable Replacement
Variable substitution is a simple and often used feature of Interchange templates. It allows you to set a variable to a particular value in the catalog.cfg directory. Then, by placing that variable name on a page, you invoke that value to be used. Before anything else is done on a template, all variable tokens are replaced by variable values. There are three types of variable tokens:
__VARIABLENAME__ is replaced by the catalog variable called VARIABLENAME.
@@VARIABLENAME@@ is replaced by the global variable called VARIABLENAME.
@_VARIABLENAME_@ is replaced by the catalog variable VARIABLENAME if it exists; otherwise, it is replaced by the global variable VARIABLENAME.
For more information on how to use the Variable configuration file directive to set global variables in interchange.cfg and catalog variables in catalog.cfg, see the Interchange Configuration Guide.