Norvig's code is gold, even back from the times of PAIP (which is still definitely a must read). His "poker" course (on YouTube) is also golden standard. Why?

Norvig's code is gold, even back from the times of PAIP (which is still definitely a must read). His "poker" course (on YouTube) is also golden standard. Why? The background in math, basic data structures and logic, so one know the range and boundaries of what is possible. Plus careful attention to details, like it is in any art.