[gdwatson]

Windows bought into Unicode hard before Unicode expanded beyond 16 bits. The consequence is that its native strings are theoretically UTF-16, but often behave like UCS-2, allowing random halves of surrogate pairs. Windows APIs reflect that, Windows filenames reflect that, and translation into UTF-8 has to reflect that -- somehow. It's not great.

Personally I'd like a world where Unicode gave up all the compromises that come with supporting UTF-16. But presumably burning all your early adopters is not a winning strategy.