For the system-provided Add action, to what row do column references used in the Only if this condition is true expression refer when I click the add-row button from a table view?
Add is a “table-scoped” action, not a “row-scoped” action. The condition is a global condition and cannot use any column references. Yes, this is awkward, but we didn’t want to introduce two kinds of actions initially. We probably will need to now. Another such example is the Export to CSV action.
@praveen, but Expression Assistant allows/does not complain about column references. So which columns is it allowing me to use?
The expression assistant is not perfect in this. It is configured here for the common case (which is a row-scoped action). But when you save, you will see an error. The right answer is to separate the table-scoped actions into a separate behavior.