The inner document of a Styled can be a Concat, but as written, unfoldD won't unfold that document. The ultimate effect, via the definition of offsetOf, is that Styled text will exceed the line length when output because renderList (BreakingSpace : xs) can't correctly measure the offset of a Styled following a BreakingSpace.

It's not readily apparent what the right adaptation is here. Sprinkling cases around like unfoldD (Styled f x) = Styled f <$> unfoldD x and offsetOf (Styled _ x) = offsetOf x works towards addresses the line-breaking issue, but that then breaks how nested styles are flattened when outputting attributed text. That suggests we have to do some sort of further intermediate step but I'd have to think pretty hard about a good way of doing that.