The goal of private modules is to define a module that cannot be trivially accessed by other modules where they are not visible to.  In this proposal, private modules work by declaring exactly which other module prefixes can access it:  defmodulep MyApp.Private, visible_to: [MyApp] do   def hello do     IO.puts "hello world"   end end  In the definition above, only MyApp and modules nested under it can access MyApp.Private. In this other example:  defmodulep MyApp.Nested.Schema, visible_to: [MyA...