You're getting an introduction, including an explanation of the parameters: https://www.2uo.de/image2.jpeg

Then short prose every now and then: https://www.2uo.de/image1.jpeg

But it's mostly the listings you can see on CTAN, as well. I actually misremembered and thought there was more explanation in the book.

What's really nice is that all glyphs are shown on a grid, next to their programs:

https://www.2uo.de/image0.jpeg