Surprisingly ITA somehow recognizes ø as a valid input if you enter for example "DEN,[space]ORD" in routing code (which is very different from "DEN,ORD"). However it just drops the comma. My interpretation would be "transfer in DEN (optional) then transfer in ORD".
BTW, can anyone explain why don't I get options with 2 stops when I enter "DEN? ORD" and why do I get options with 3 stops when I enter "DEN ORD"?
For example from NYC to SFO.