http://www.dotnet-tricks.com/Tutorial/angularjs/4E7J080914-Understanding-AngularJS-$watch(),-$digest()-and-$apply().html

(Shailendra Chauhan) AngularJS has a powerful data binding mechanism. When you do changes in a variable on the $scope object within your view, the $scope object auto-magically updates itself. Similarly, whenever the $scope object changes, the view updates itself with the new value.

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