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 sin

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/?the_regex=%5E(((https%3F%7Cftps%3F)%3A%5C%2F%5C%2F)%7Circ%3A%5C%2F%5C%2F%7Cmailto%3A)(%5B%5Cw%3F!~%5E%5C%2F%5C%5C%23%24%25%26'()*%2B%2C%5C-.%5C%2F%3A%3B%3C%3D%40%5D*%5B%5Cw~%5E%5C%2F%5C%5C%23%24%25%26'()*%2B%2C%5C-%5C%2F%3A%3B%3C%3D%40%5D)&the_subject=mailto%3A%5Ep81 https://blog.robertelder.org/regular-expression-visualizer/?...