This is absolutely phenomenal. This is how a lot of education should be. What blew my mind is how the author gradually increases the density of subject matter

This is absolutely phenomenal. This is how a lot of education should be. What blew my mind is how the author gradually increases the density of subject matter, going from the basics to the most advanced concepts in such a way that things just flow naturally. To say nothing of the interactive-ness of the page itself, which helps explain things exceptionally. Superb post.