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 {TAIL ~ the thickness} of the acetal material portion and the acid resistant material portion is substantially equal to the certain overall thickness 
of
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 { TAIL ~ the thickness } of the acetal material portion and the acid resistant material portion is substantially equal to 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 REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH