docs: function() {
    return {
      require: ['ngModel', '^?form'],
      controller: NgModelController,
      link: function(scope, element, attr, ctrls) {
        // notify others, especially parent forms
  
        var modelCtrl = ctrls[0],
            formCtrl = ctrls[1] || nullFormCtrl;
  
        formCtrl.$addControl(modelCtrl);
  
        scope.$on('$destroy', function() {
          formCtrl.$removeControl(modelCtrl);
        });
      }
    };
  }