Tony Morris

Right. My take: "The library defines and exposes a small, simple, orthogonal core, that it uses to define the library functions."

This again refers to implementation. Could we spot a good/bad API without looking at its implementation?

John's criteria isn't about just library API, it's about the library as a whole.

Then could we tell a good library without looking at its implementation?

Definitely no, I know tons of great libraries without any documentation... Just look at what Kmett is producing.

Don't limit yourself to judging just by documentation. You can make a judgment based on the API and observable behavior.

Had an interesting discussion with @dibblego lately about writing a tool to automate this by analyzing sources.

I accept John's points 1. and 3. as self-evident. From a user's perspective, why should I care about 2.? Probably because it manifests as something I care about. What is that something and what's the causal link from orthogonality to that something.