I really have a feeling that I'm overthinking this WAY TOO MUCH, and the answer is going to be something simple. If that's the case, then I think that makes this a really good kata. Reminds me that some times I have the tendency to over-complicate my programs in lieu of a simple approach. Now, back to this madness...

Hey, I like the way you solved this. I was wondering about the underscore as the first parameter of the callback function to the replace method. Is that a variable to the regular expression? You can put whatever you want for that parameter? Sorry if the question is stupid. I'm relatively new to this.
Thanks!

https://www.youtube.com/watch?v=ljNi8nS5TtQ

At about 30 minutes into this video, he goes over the exact same thing that this Kata is trying to teach. It helped me to
not only complete the Kata, but to understand exactly what was going on.