['A'..'M'], ['N'..'Z'],
['a'..'m'], ['n'..'z'],
);
-my @chars2 = (@chars, ['_']); # trailing character (extended set)
+my @chars2 = (['_'], @chars); # trailing character (extended set)
print '<table><col>';
print qq'<colgroup span="$_">' for map {scalar @$_} @chars2;