Occurs when a finger touches the screen while the finger is over this element.
Assembly: PresentationCore (in PresentationCore.dll)
By default, the PreviewTouchDown and events do not occur until a finger touches the screen and moves. Pressing a finger on the screen and holding it without moving it causes the press and hold behavior of a Stylus. The press and hold behavior is equivalent to a mouse right-click.
Available since 4.0