The EZ Screen runs the top-most criteria first and then proceeds down the list. Priority allows you to specify the order in which your screen is run.
Simply assign a 1 - 13 value to the criteria in the order that you want the screen to be run. This enables you to decide which criteria is screened first and so on.
Because the EZ Screen runs screens on a percentage basis, it is possible that when you change the priority, you will have a different set of tickers.