No prob. This is a quote from the investor call:

Mike, this is Scott Haralson. Yes, quick comment on the conversion component. We did in this order 319s, 320s and 321s, so the 320 family. However, we do have conversion rates up and down the spectrum of what Airbus offers through the 19, 20, and 21 as well into the 220 if we would like to do that. That's just a mechanism, and the contract -- not a hint to our desire to do that at all. Our plan is to operate the 320 family of aircraft.

I couldn't find any reference to XLR in the investor call now that I looked for it but I did read it somewhere (sorry can't find it rn) that they can flex up to XLRs too but, again, as of now that's not the plan.