sub tt {
  my( $cookie, $param ) = @_;
  my $str = '(' . (defined $cookie ? $cookie : 'undef');
  $str   .= ',' . (defined $param  ? $param  : 'undef') . "):\t";
  $str .= $cookie
          # I quickly realized it was necessary to test this here
          ? ( ( $param and $param =~ /^\d{1,2}$/ ) ? $param : $cookie )
          # and I had to place a few more parens
          #: ( $param ? ($param and $param =~ /^\d{1,2}$/) : 5 );
          # UPDATE: the above line was horribly translated from Grandfathers.
          # It is corrected below, which also works when the same nested
          # ternary idea (substituting /^\w{1,6}$/ for example) is used to
          # parse textual data.
          : ( ( $param and $param =~ /^\d{1,2}$/ ) ? $param : 5 );
          # END UPDATE
  $str .= "\n";
  return $str;
}

print tt( 4, 3 );
print tt( 4, 333 );
print tt( 444, 333 );
print tt( 2, undef );
print tt( undef, 1 );
print tt( undef, undef );