I recently discovered #regex on freenode, where the author of regex101.com is hanging, I asked him about this issue since it's bothering me (regex101.com handles the \K example and the (?=) lookahead example correctly).
What jaytea quoted from the manpage is exactly what the author is doing, and is what should be done.
With the recent addition of the custom /F modifier which basically makes regexes working as they should regarding capturing group matching 0 time, I think it would be a good idea to try to implement the manpage recommendation right now only when /F is provided, and possibly then supports that implementation even without /F, later on.
