But I doubt someone new to regexps would understand what "looks like" means in that context. For instance they might think "ok, so something like 'abc@efg.xyz' matches, even though it's not a real email address." They might not think to consider that a full sentence like "hey, I'll see you tomorrow @ 2. Can't wait!" also matches.

That said, perl one-liners are certainly useful so thanks to the OP for putting this together. I just think it would add a lot of value to include examples of where one is likely to go wrong.