How to include an attribute from the MAIN (primary) attribute group in an assignment business rule?

 I want to base a business rule on the value in Secondary Default Ind.  My rule is defined at the ICC level, not a particular attribute group, and it is defined at the item level (not item org).  In the IF part of the rule, I try the internal name of -> MAIN  but that does not validate.  The R12 PIM Install Guide has an example of -> Item_Primary.<attrib name>  in the section Administering Item Business Rules 6-3, but that does not validate for me either.  What is the syntax for the primary/main attribute when you want to set a value of an attribute in a user-defined group based on the value of an attribute on the main page?