How do you reference the export value of a combo box item?

Good question. There's no simple way. The most direct way would be to use the currentValueIndices property and the getItemAt method to get it, but that doesn't update until after the validation event, so if you try it you'll get the value from before the change.

The only approach that I found to work is to basically iterate over all the items in the field (using numItems and getItemAt), comparing them to event.value, and if you find a match then use getItemAt again to get the export value of that index.