gistfile1.js

Link: {
  Toggle: Behavior.create({
    initialize: function(toggleElement) {
      this.addText = this.element.innerHTML;
      this.cancelText = 'cancel';
      this.toggleElement = $(toggleElement);
    },

    onclick: function(event) {
      var element = event.element();
      var text = element.hasClassName('add') ? this.cancelText : this.addText;
      element.update(text);

      element.toggleClassName('add');
      element.toggleClassName('cancel');

      (this.toggleElement || element.next()).toggle();
    }
  })
}