This isn't about getting something to work without knowing what happens inside, tho, this is about defining what happens inside without knowing how it's expected to work. I doubt that's how anything was developed.

It should probably be added to the description that the expected value will be given at each failed attempt. Generally, a submission at Codewars is a piece of code that you expect solve the problem. I don't think anyone here is naturally inclined to submit a stab in the dark just to find the pattern, unless this is specified.

Surely, this isn't right? Demo

It's not about IP's that wouldn't work, but non-IP's that would work. This expression allows an IP like 299.299.299.299, which is in fact invalid.

Your pattern allows all valid IP's, but it doesn't reject all invalid ones. For instance 1.299.3.4 and 1.02.3.4 are both invalid, but accepted by your pattern.