It's the first time I saw anyone acknowledge this profound insight: sometimes, writing a practically useful API entirely at the same level of abstraction simply isn't possible.
Looks like it's available here, now:
Edit: sorry this was replied to smunz's comment.
Not to leave HN, just to complement it ;)
That was the first thing I though on starting to read this. How do they know they've actually got it right? Feedback from users?