Maybe this has been widely discussed here and I'm the last one to learn it. Wouldn't be the first time.....
In talking to a SWA agent this morning, I was reading my confirmation code to her and said..." I don't know if the next digit is a zero or the letter 'O' ".
She said that WN doesn't use zeros or ones in their confirmation codes so as to not confuse them with the letters o and i. Only numbers that will appear are 2 through 9.
So next time you see a confirmation code such as RFZOGl, you can be confident they're all letters. Saves time when typing in your confirmation to get an advance boarding pass.
FYI for anybody who wasn't aware of this.