Assembly: PresentationFramework (in PresentationFramework.dll)
The default value of this property depends which version of WPF that your app targets. If your app targets WPF 4.0 or earlier, the default is false. If your app targets WPF 4.5, the default is true. If you use this property to change the behavior of WPF, you must change the property’s value early in the app’s lifetime, such in the constructor of the class that inherits from Application. After the value is read, you cannot change it again.