title: Hide the child control when it's transformed out of its parent grid or border
body: <p>Let's say we have a grid with a TextBlock in it. Now if I do some RenderTransform which makes the TextBlock appear outside of the grid, the TextBlock is still visible. My question is simple: how to automatically hide the part of the TextBlock that's outside of the grid? (In other words, how to make the grid act like a visual bound of its child?)</p>