Retrieving the transaction number on user notes using a scripted search

My company's transactions are almost entirely drop-shipments, so it would be nice to be able to view on the purchase order any user notes that had been entered on the related sales order . I am trying to write a script that will copy notes from the sales order and enter them on the related purchase order. My first step would be to create a scripted search that would return the notes' sales order numbers, which in turn would be used to dynamically filter the related purchase orders to copy the notes to. However, I was surprised to see in