typedef enum {
    MPIIdnFieldINVALID,

    MPIIdnFieldNUMBER,
    MPIIdnFieldNAME,
    MPIIdnFieldATTRIBUTES,
    MPIIdnFieldUNIT,
    MPIIdnFieldMINIMUM,
    MPIIdnFieldMAXIMUM,
    MPIIdnFieldDATA,

    MPIIdnFieldALL,
} MPIIdnField;

The IdnField enumeration is a list of all the different fields that comprises an IDN.