Well, I don't have the experience required judge on the usefulness or frequency of searches with invalid indexes, but given how messy string manipulation can get, I can see how it would be useful, so I'll concede the point.

I'm sure its not what you meant when you said `nothrow`, but just to avoid any confusion, I'll point out anyways that a `nothrow` function is allowed to throw errors. So if you meant actual `nothrow`, that would not have been a problem.