The (?:stuff) part is for a non-capturing group which I didn't add support for. Maybe in the near future. That would be one of the easiest features to add since the tool also doesn't support backreferences yet.

Edit: Actually, since the non-capturing group part doesn't add much here, you can just remove the '?:'s and this works:

https://blog.robertelder.org/regular-expression-visualizer/?...