Ask HN: Clean standard library implementation with great comments for learning?

I am a junior dev and want to up my understanding of various things that go into the typical standard library for a programming language. Basically I want to learn by reading the entire standard library of a programming language and getting a deep understanding of how to use it.

In your opinion, which programming language implementation includes a nicely commented stdlib with clean code? (i.e. so that I can actually read it?)

From my own little research, the Go standard library seems to be a good contender, any others?