Wouldn't "Nee, tot ziens" also be correct?
It might be that "bye" is given as a translation for "doei" because "doei" is less formal than "tot ziens". I'm not sure if the distinction is as strong between "bye" and "good bye", but it may be useful for teaching the difference in Dutch.
I was taught that DOEI is a Brabants expression.
No, not at all. Maybe you are confusing it with "houdoe".
From my experience, 'doei' isn't an expression that is used in Belgium at all...
My boyfriend is from Holland, and I really listen him saying almost everyday this expression. Am really getting confused.
When would you use dag? It sounds very informal.
Doei is more informal, dag seems to be more common. Besides is both bye and hi, if I'm not wrong