in a dynamic table, can instance manager tell the index of current row instance?

Script Dependencies and "recalculate()"

I follow the example here, and use it to make a dynamic table. The +/- button now work as my Add/Delete row button.

Learnt from the guide, I can use instance manager and add or remove instance of row. Now I want to know which row I'm editing now, so that when there is data in the rows other than the first row, it pops up an alert to remind me to fill in the first row as a preliminary.

Code of instance manager that works in my local:

var oTargetSubform = addButton.parent.repeatingTable.repeatingRow; // The subform or table row the controls are intended to manipulate.

var oManager = oTargetSubform.instanceManager; // Get the instance manager.

while I guess the property I should refer to is oManager.index, it always return 0, yet I don't find the definition of "index" in Designer 11 document: Adobe LiveCycle ES4 * instanceManager