From Xojo Documentation
A "hidden" identifier associated with the item identified by the Row parameter. The first row is numbered zero.
If you want to compare the value of RowTag to another value, you must first convert the value of RowTag to that data type.
This example populates the RowTag identifier with a sequence number.
recID = ComboBox1.RowTag(1) // ComboBox inherits from PopupMenu so it also inherits the RowTag method
Displaying the RowTag of the selected menu item: