This is similar to my previous efforts (wordEnds and repeatEnd): as a mental exercise, I want to solve this toy problem using regex only.

Description from codingbat.com:

Given a string and a non-empty word string, return a version of the original string where all chars have been replaced by pluses ("+"), except for appearances of the word string which are preserved unchanged.

plusOut("12xy34", "xy") ? "++xy++"
plusOut("12xy34", "1") ? "1+++++"
plusOut("12xy34xyabcxy", "xy") ? "++xy++xy+++xy"

There is no mention whether or not to allow overlap (e.g. what is plusOut("+xAxAx+", "xAx")?), but my non-regex solution doesn't handle overlap and it passes, so I guess we can assume non-overlapping occurrences of word if it makes it simpler.

In any case, I'd like to solve this using regex (of the same style that I did before with the other two problems), but I'm absolutely stumped. I don't even have anything to show, because I have nothing that works.

So let's see what the stackoverflow community comes up with.