19.1.1. Semantic Changes Starting in MPI-4.0

• MPI_COMM_DUP and MPI_COMM_IDUP no longer propagate info hints from the input communicator to the output communicator. This behavior can be achieved using MPI_COMM_DUP_WITH_INFO and MPI_COMM_IDUP_WITH_INFO.

• The default communicator where errors are raised when not involving a communicator, window, or file was changed from MPI_COMM_WORLD to MPI_COMM_SELF.