It really irks me when I see some design/architecture decisions other developers have made but there's no technical explanation. What packages did they use? What challenges did they face? What trade-offs were made? I'll go over some more specifics in this post.
He recaps some of the things covered in the previous post first, ensuring everyone is on the same page. He then gets into the concept of "bundles" and how they encapsulate functionality. From there he talks about commands, controllers, dependency injection and lots of other topics, each with their own summary and a bit of code where needed for clarification.