[angularjs] AngularJS access parent scope from child controller

Super easy and works, but not sure why....

angular.module('testing')
  .directive('details', function () {
        return {
              templateUrl: 'components/details.template.html',
              restrict: 'E',                 
              controller: function ($scope) {
                    $scope.details=$scope.details;  <=== can see the parent details doing this                     
              }
        };
  });