application.js

$.fn.subnavTabs = function(options) {
  var opts = $.extend({}, $.fn.subnavTabs.defaults, options);

  return this.each(function() {
    var self  = $(this),
        tabs  = $(self.attr('rel')),
        items = self.children('li'),
        links = items.children('a')
        show_active = function() {
          tabs.children('div.box').hide();
          $(items.filter('.active').children('a').attr('href')).show();
        },
        set_active = function(obj) {
          items.removeClass('active');
          obj.parent('li').addClass('active');
        };

    show_active();

    links.click(function() {
      set_active($(this));
      show_active();
      return false;
    });
  });
};
$.fn.subnavTabs.defaults = {};