The $XABTRM_STORE macro moves user-specified values into fields
    of the specified XABTRM. The expanded $XABTRM_STORE code executes
    at run time on a previously initialized (allocated) XABTRM, in
    contrast to the $XABTRM macro, which initializes a XABTRM at
    assembly time. The $XABTRM_STORE macro must reside in a code
    program section.

    Format

      $XABTRM_STORE  XAB=xabtrm-address,

                     ITMLST=item-list-address,

                     ITMLST_LEN=#item-list-length,

                     NXT=next-xab-address