Coke...Zero??

O.k., so can anyone explain to me what makes a Coke Zero be zero? I mean, I know it has zero calories, but it tastes EXACTLY LIKE REGULAR COKE! So what does it have?

Then again, there's a part of me that almost doesn't want to know. It's one of those too-good-to-be-true things. It tastes good, it's got zero calories, do I really need to know anything more? So it may be rotting my insides...eh...insides-shminsides. I once heard someone say that if you pour a Coke down a drain it basically does the same as what pouring Draino down the pipe would do. So I'll have clean "pipes"! How's that for looking at the glass half Coke Zero full? ;)