This is quite a lazy answer for top-rated. The comments below mention it will accept numbers etc, which I think isn't even that bad compared to the fact it will accept spaces and slashes, etc.

It will even accept joe@@example.com

This is a little naughty; it will accept things like 12758493@432143214321.4321432143214321

I agree it should return a Rational not nil especially since this is meant to emulate the ** operator.

This will accept emails like "joe@example.com." or "joe@..."

Sorry! but what is expected result for power(8, -2) ?
Both 0.015625 and (1/64) are wrong