How does ng-selected work?

HTML

<div ng-app="MyModule">
  <div ng-controller="MyCtrl">
    <select name="quarter" ng-model="Quarter" ng-selected="Quarter"
        ng-options="Quarter for Quarter in Quarters" >
      {{Quarter}}
    </select>
  </div>
</div>

JavaScript

angular.module('MyModule', [])
  .controller('MyCtrl', function($scope){
      $scope.Quarter = 'Q2';
      $scope.Quarters = ['Q1', 'Q2', 'Q3', 'Q4'];
  });