Multiple headboxes could be controlled, such as when different headboxes are used to produce {TAIL ~ different layers} of {HEAD ~ a multi layer sheet} 
Multiple headboxes could be controlled , such as when different headboxes are used to produce { TAIL ~ different layers } of { HEAD ~ a multi layer sheet }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD