Using in direct sunlight

Don't. You can damage the display.

Link, please? I didn't known sunlight could damage an iPad display.

It won't, but it will result in overheating and that message will pop up on the screen and the device will be inoperable until it cools down.

What's the message? Is it if the iPads internal temp gets above the operating parameters? Can't imagine using it long enough outdoors for that to happen . . . and it would certainly depend upon the location and the time of day. But it certainly could happen in a parked car, which Apple cautions against on one of it's battery support pages, IIRC.

It is the yellow triangle with the exclamation and a message that the device has overheated. I got it once on my iPhone on an airplane sitting on the tarmac and also got it on my iPad last summer. Here in Texas it only took about 25 minutes and I was not in direct sunlight. The person I stood in line with when I purchased mine took hers out in sunlight just to try reading with it. In direct sunlight it triggered the thermal warning in less than 10 minutes.

I recommend the Nook (the black and white model) or the Kindle if you are going to read in sunlight. My former Chief and his wife have used theirs on the beach many times.