传递把子指令时，父指令控制器未定义

I asked general question here in this post. I've got answer with working example; however when I try to use this example to modify existing code, I get error. See my code below and in this Plunker page.

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.5.3/angular.min.js"></script>
<div ng-app="myApp">
  <tmp-menu ng-disabled="true">
    <tmp-menu-link></tmp-menu-link>
    <tmp-menu-link></tmp-menu-link>
  </tmp-menu>
</div>

JavaScript(AngularJS):

JavaScript(AngularJS):

angular.module('myApp', [])
.controller('MyDirectiveController', MyDirectiveController)
.directive('tmpMenu', function() {
  return {
    restrict: 'AE',
    replace:true,
    transclude:true,
    scope:{
      disabled: '=?ngDisabled'
    },
    controller: 'MyDirectiveController',
    template: '<div>myDirective Disabled: {{ disabled }}<ng-transclude></ng-transclude></div>',
    link: function(scope, element, attrs) {


    }
  };
})
.directive('tmpMenuLink', function() {
  return {
    restrict: 'AE',
    replace:true,
    transclude:true,
    scope:{
    },
    required:'^^tmpMenu',
    template: '<div>childDirective disabled: {{ disabled }}</div>',
    link: function(scope, element, attrs, MyDirectiveCtrl) {
      console.log(MyDirectiveCtrl);

      scope.disabled = MyDirectiveCtrl.isDisabled();

    }
  };
})

function MyDirectiveController($scope) {
  this.isDisabled = function() {
    return $scope.disabled;
  };
}

内部指令 tmpMenuLink ， MyDirectiveCtrl 是未定义. 为什么会这样?

Inside directive tmpMenuLink, MyDirectiveCtrl is undefined. Why is that?