        /// <summary>
        /// Gets or sets the plane representing the mouse cursor's X position in 3D space.  This forms
        /// a plane such that if it were projected back to the screen it would intersect the mouse's
        /// X position along the Y axis of the screen.  This is updated automatically by 
        /// DefaultRenderContext based on the World, View and Projection properties of the current render context.
        /// </summary>
        /// <value>The plane representing the mouse cursor's X position in 3D space.</value>