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