That is a much better way to write it, except that even using $+[0] rather than pos, the /g is still required? I do not pretend to understand that, but it is so.

Which also explains why it broke when I tried to use $-[0] originally. I would never have thought that @- and @+ where dependant upon /g? Is that a bug?

I mentioned I was embarassed by the code. My only excuse is that it evolved into the state where it worked and I've been concerned with more fundemental restructuring.

In-situ, with the /g, it makes no difference to the functioning of the code--which means your version is now in the real code.

I'm not sure what you expect $pos and $first to be when the match fails...

Nothing! If the match fails, there is nothing (or nothing further) that can be done in the call and the code just returns to the caller. If the match fails, I do not have any break point upon which to decide to output anything, so all I can do is wait until more of the string accumulates. Ie. the next call, or the one after that.