=over =item $a =item $b X<$a> X<$b> Special package variables when using C<sort()>, see L<perlfunc/sort>. Because of this specialness C<$a> and C<$b> don't need to be declared (using C<use vars>, or C<our()>) even when using the C<strict 'vars'> pragma. Don't lexicalize them with C<my $a> or C<my $b> if you want to be able to use them in the C<sort()> comparison block or function. =back