The point is to implement gradually. For example, in the concepts covered in part 1, multiple parents was not required, hence it was left. It should make sense

The point is to implement gradually. For example, in the concepts covered in part 1, multiple parents was not required, hence it was left. It should make sense to the reader why something was implemented and why it does what it does. Its concepts might apply to other VCS. But that is immaterial, Git is what we are trying to understand here.