{HEAD ~ The flexible sheets} are attached to structural members, that is, to purlins beneath {TAIL ~ the roof panels} 
are attached beneath
{ HEAD ~ The flexible sheets } are attached to structural members , that is , to purlins beneath { TAIL ~ the roof panels }
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL