AngularJS classMap directive

HTML

<div ng-app="myModule">
  <div ng-controller="myController">
      <div ng-class="{'red' : _red, bold : _bold,'multiple things' : shouldUseMultiple()}" >ng-class base</div>
      
      <input type="checkbox" ng-model="_red">red</input>&nbsp;&nbsp;
      <input type="checkbox" ng-model="_bold">bold</input>
      <br />
      _red: {{_red}}
      <br />
      _bold: {{_bold}}
      <br />
      should use multiple: {{ shouldUseMultiple() }}

  </div>
</div>

CSS

.red
{
    color:blue;
}

.bold
{
    font-weight: bold;
}

.multiple
{
    font-size: 72pt;   
}

.things
{
    background-color:orange;
}

JavaScript

var myModule = angular.module('myModule', []);

myModule.controller('myController', function($scope) {

    $scope._red = true;
    $scope._bold = false;
    $scope.shouldUseMultiple = function(){return this._red ^ this._bold;};
});