Always challenging to grab urls, because not all urls start with www. We could have something like https://docs.example.com or a non-url with a www.notaurl.

What I suggest is that we include the option for www.etc in addition to https, and maybe create a global for creating a vector of acceptable regexes for parsing. That way you can massage the settings as you realize you need more or less from the documents.

I can't imagine you wanting to archive something from gopher:// but who knows? :)

right, obviously you can't require www. but I think www.notaurl would be pretty rare (the gh URL parser agrees ;)
So I think having the configurable vector would be great, but relaxing the default to allow URLs to start with either https? or www. makes sense and seems to be what forums parsers do.

Found this regex for the solution: https://www.regextester.com/93652 and it will be on the next commit to the PR.

Notice that it's not perfect - it will not capture something like yahoo.com, but much more flexible that the previous regex.

That looks good -- note that it will catch yahoo.com (there's a ? after the whole https/www monster). We can test & see if that's too relaxed and if so, remove that part. or turn it into something like
(https?\/\/(www\.)?|https:\/\/) which is more restrictive
Talking of monster, please use (https?:\/\/(www\.)?) for the first capturing group instead. No need to make this so long

Ooops. Nice job by them. I do need the monster unfortunately, because we want to return the whole url for parsing. The shortened version will only return the prefixes.

I just mean for the beginning, so the whole thing would be
^(https?:\/\/(www\.)?)?[a-z0-9]+([\-\.]{1}[a-z0-9]+)*\.[a-z]{2,5}(:[0-9]{1,5})?(\/.*)?$
That should be equivalent

Well, if you think that's bad, remember that R requires a double backslash for escaping regex characters! Argh! :)