In the MPI_T return code Table (P589), there are Return Codes for Datatype Functions: MPI_T_ENUM_* MPI_T_ERR_INVALID_INDEX The enumeration index is invalid or has been deleted. MPI_T_ERR_INVALID_ITEM The item index queried is out of range (for MPI_T_ENUM_GET_ITEM only) Why we used "enumeration index" here? Since in the standard, it is called a handle. And why designed MPI_T_ERR_INVALID_ITEM specially for MPI_T_ENUM_GET_ITEM? In my view, there should be MPI_T_ERR_INVALID_ENUM, MPI_T_ERR_INVALID_INDEX respectively. --Junchao Zhang