Note that $% is a special variable and is interpolated in the  [@#$%^&+=] regex character set. Escape it with a  \ (backslash) instead.

>perl -wMstrict -le
"my $cs1 = qr{ [ab$%cd] }xms;
 print $cs1;
 my $cs2 = qr{ [ab\$%cd] }xms;
 print $cs2;
"
(?msx-i: [ab0cd] )
(?msx-i: [ab\$%cd] )
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