The interesting bit here is at the end. Theenvironmentsection sets an environment variable in the Docker registry container with the path/data. The Docker registry app knows to check this environment variable when it starts up and to start saving its data to the/datafolder as a result. ...
For HoI4, we are leaning more towards the Doctrine paths you may remember from HoI2 than the mix-and-match of HoI3. We have 4 main mutually exclusive Doctrine paths which nations can research. Each path also has one or more mutually exclusive choices to further differentiate the doctrines ...