The region also includes an acid resistant material portion provided directly over the acetal material portion in an amount such that {HEAD ~ the combination} of the thickness of the acetal material portion and the acid resistant material portion is substantially equal to {TAIL ~ the certain overall thickness} 
is substantially equal to
The region also includes an acid resistant material portion provided directly over the acetal material portion in an amount such that { HEAD ~ the combination } of the thickness of the acetal material portion and the acid resistant material portion is substantially equal to { TAIL ~ the certain overall thickness }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL