Not as a real document. But gdb exists partially to supplement this lack of documentation. It can definitively help you understand what is going on during the initialization stage of the MPI library.
To answer specifically your question about MPI_COMM_WORLD, take a look in ompi/communicator/comm_init.c around line 98.
I am searching for something of a guide to OpenMPI developer. Specifically, I need to understand how the OpenMPI is initialized. For example how the COMM_WORLD is initialized. Is there any help in this regard?
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