XML reference assistance

Hello, I am trying to fulfill two scenarios by using the XML ref guide:

1) If an item has already been scanned/entered and already exists as a line item in the POS, then any subsequent scan will increment the counter.

PurchaseOrder.Entry.Lookupcode exists PurchaseOrder.Entry.Lookupcode ++

2) Sort the item list by Item Lookup Code (ILC)

(Entry.X.Lookupcode &gt Entry.X+1.Lookupcode) Move item

Can someone provide some further information on the functionality and operators that can be used with the IF and FOR loops/conditionals within a receipt format?

Thank you for your time, Kevin Fisher