my $s = q[<IL.Check/>];
my $r = q[<&#x221a;>];

print "Old word: $s\n";
$s =~ s/$s/$r/;
print "New word: $s\n";

##</code><code>##

my $s = q[<IL.Check/>];
my $r = q[<&#x221a;>];

print "Old word: $s\n";
$s =~ s/\Q$s\E/$r/;
print "New word: $s\n";