sap_anchor
if (push.sap_anchor == (i + 1))
pushp->sap_anchor = 0; /* by default, no anchor */
if (pushp->sap_anchor != 0) {
pushp->sap_anchor = npush;
*anchor = push.sap_anchor;
push.sap_anchor = *anchor;
push.sap_anchor = 0;
ap->ap_anchor = sap->sap_anchor;
sap->sap_anchor = ap->ap_anchor;