I am migrating a Browser Application from Version 8 to AA.
In v8 I used a grid linker component to link a parent and child grid pair.
Within the grid linker component I was able to specify an override to the DropdownBox filter property for fields on the child grid.
In the override settings I had
field_info[4].DropDownBox.Filter = "School = " + quote(pgrid.session.CurrentSchool)

Using the now recommended linked grid facilities, the grid linker is redundant.
I have tried to use the filter property directly in the child grid. The Filter Builder has the facility to include a variable in the filter expression. However you have to choose from a list of variables, and I have not been able to find how to get my session variable into this list.

How do you get session variable into this list?
or alternatively, Is this the best approach to applying a run-time filter to a field on my subordinate grid.

Thanks in advance to anyone that can provide guidance.