Curious where Apple warns you not to do that. Seriously, we have users who this has happened to, and I don't believe they were in full sunlight. They work in an office.
You had me curious so I did some searching; I did find a few support threads discussing this sort of problem; consensus seems to be that it's not burn-in (which I'd find really surprising: I sit outdoors or by windows and work in bright light as often as possible (seasonal affective disorder yay) so I'd expect if actual screen burn-in was a thing, I'd have experienced it by now.) Instead it's pressure damage:
> If you carry laptop around and it's squished between books or whatever, that's how you get that. My first unibody macbook developed this issue. Now I use a hard case.
> What I suspect happened here is you had laid something heavy on top of your air so the logo disk in the lid embossed the defuser sheets.
