Wow. Did not expect you can just hide arbitrary data inside totally normal looking strings like that. If I select up to "Copy thi" and decode, there's no hidden string, but just holding shift+right arrow to select just "one more character", the "s" in "this", the hidden string comes along.

Based on vim's word wrapping (which shows blank spaces instead of completely hiding it), they're being rendered at the end of the line. So if that is accurate it kind of makes sense that for UI-based interactions to be a one-character offset.