Tablesorter: sort checbox columns

gistfile1.txt

 // add tablesorter parser to be able to sort on checkboxes
    $.tablesorter.addParser({
        id: 'checkbox',
        is: function (s, table, cell) {
            return $(cell).find('input[type=checkbox]').length > 0;
        },
        format: function (s, table, cell) {
            return $(cell).find('input:checked').length > 0 ? 0 : 1;
        },
        type: "numeric"
    });