code: function onchange(evt) { // called in context
      var ctrl = evt.target;
      if (ctrl.parentElement === this.el) {
          if (ctrl.value === 'subexp') {
              this.children.push(new FilterTree({
                  parent: this
              }));
          } else {
              this.add({
                  state: { editor: ctrl.value },
                  focus: true
              });
          }
          ctrl.selectedIndex = 0;
      }
  }
docs: Some event handlers bound to FilterTree object