The B2 edition of this book is out. The new chapter is dedicated to Supervisors. These are correctly described as Lifecycle components.
This is the first time that I have seen the new DynamicSupervisors being used.
Minor note the parameter in
Lifecycle/lib/mastery/boundary/quiz_session.ex for select_session/1 has changed to name from session.
Similarly for answer_question/2
The code samples now clearly state where the code is to be added.
There was a minor typo and some missing code that breaks the final iex session.
Current code can be found at: https://github.com:chriseyre2000/designing_elixir
Developer Rants 