5.1.2.0.1 Caching.

Communicators (see below) provide a ``caching'' mechanism that allows one to associate new attributes with communicators, on a par with MPI built-in features. This can be used by advanced users to adorn communicators further, and by MPI to implement some communicator functions. For example, the virtual-topology functions described in Chapter 6 are likely to be supported this way.

MPI-Standard for MARMOT