Let's assume that you need to show the status of a user and you have several possible CSS classes that could be used. Angular makes it very easy to choose from a list of several possible classes which allow you to specify an object list that include conditionals. Angular is able to use the correct class based on the truthiness of the conditionals.
Your object should contain key/value pairs. The key is a class name that will be applied when the value (conditional) evaluates to true.
Angular will check the $scope.user object to see the active status and the level number. Depending on the values in those variables, Angular will apply the matching style to the < span >.