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