A complete roll of wrapping material comprises {HEAD ~ several wrapping portions}, which are held and released at {TAIL ~ their lateral ends} 
are released at
A complete roll of wrapping material comprises { HEAD ~ several wrapping portions } , which are held and released at { TAIL ~ their lateral ends }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL