title: What are WPF Preview Events?
body: <p>I have been looking for descriptions of events "Preview******" like every element has events KeyDown and PreviewKeyDown. What is difference (not that one is attached event and one is not, the real conventional difference and programming way difference)</p>
  
  <p>In any class derived from Control, you can override both methods.. OnKeyDown and OnPreviewKeyDown, now I am writing my custom control, which method shall I use? And whats difference between both of them.</p>