It's been a few years, but from memory:

IIRC you could e.g. install new keys, but not quite list them (somehow only almost), and you couldn't remove them again.

Amusingly you could also tell the API was developed by three different people, who preferred different API styles (I remember one was fond of callbacks, the others apparently not so much). Reading the documentation was pretty funny because you got pretty good at spotting which functions had been created by Alice, Bob or Charlie. That was the only thing that was fun about it :-)