Makes sense. I've never been asked to make such an exercise in real time, most of the time that would be a take home task - but I understand if someone wants to do that. Still it would be weird to demand that a candidate uses Google, wouldn't it?
I picked e-mail validation as an example precisely because it's something even experienced developers would be well advised to google if they want to get it right :)
Of course, if someone can get it right off the top of their head, more power to them!
