When defining an extended composition on an existing class, is it the active instance of that class visible to template code in the extended sub-object (eg for generating a list of values), and if so, how do you access it? In script generation, you can use ActiveSelection, but this does not seem to be available in the context of a form.
The specific problem I am trying to solve is adding support for filtered indexes to the SQL 2012 DBMS. The simple approach would be to add a free-text attriute for the filter condition, but I would prefer to have the columns referenced in the condition linked to the table column definition. This means creating an extended sub-object with an attribute whose list of possible values is the column collection for the associated table. Is this possible?