maybe this is what you need: 
my $cn = qr/chapnum/;
my $cp = qr/chapter/;
$str1 =~ s#(1</$cn>\s*</$cp>\s*)<x>(<$cp>\s*<$cn>1A)#$1$2#s;

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In reply to Re: Pattern matching problem by mantadin
in thread Pattern matching problem by Anonymous Monk

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