Key handling interacts with other platform features such as commanding and text composition. The KeyDown event is a lower-level text input event that might not behave as expected on certain controls. This is because some controls have control compositing or class handling that provides a higher-level version of text input handling and related events.
This event creates an alias for the Keyboard..::.PreviewKeyDown attached event for this class, so that PreviewKeyDown is part of the class members list when UIElement is inherited as a base element. Event handlers that are attached to the PreviewKeyDown event are attached to the underlying Keyboard..::.PreviewKeyDown attached event and receive the same event data instance.