The $RAB macro allocates storage for a RAB and initializes
    certain RAB fields with defaults and user-specified values.
    You cannot use this macro within a sequence of executable
    instructions. No value is returned for this assembly-time
    operation.

    Format

      $RAB  BKT=bucket-code-number,

            CTX=user-context-value,

            FAB=fab-address,

            KBF=key-buffer-address,

            KRF=key-of-reference-number,

            KSZ=key-size,

            MBC=multiblock-count-number,

            MBF=multibuffer-count-number,

            PBF=prompt-buffer-address,

            PSZ=prompt-buffer-size,

            RAC={KEY|RFA|SEQ},

            RBF=record-buffer-address,

            RHB=record-header-buffer-address,

            ROP=<ASY BIO CCO CDK CVT EOF EQNXT ETO FDL KGE KGT LIM

            LOA LOC NLK NXR NXT PMT PTA RAH REA REV RLK RNE RNF RRL

            TMO TPT UIF ULK WAT WBH>,

            ROP_2=<NQL NODLCKWT NODLCKBLK>,

            RSZ=record-size,

            TMO=time-out-number-of-seconds,

            UBF=user-record-buffer-address,

            USZ=user-record-buffer-size,

            XAB=xab-address