I was reading an old document for What's New in version 10, and I found this feature being introduced to aid working in the 2D sketch environment:-     Reference Snapping to 3D - During creation and modification of 2D elements, users can now reference 3D geometry without the need to project the geometry to the 2D Sketch. Holding the cursor over a 3D element for a brief second will place a reference indicator to the 3D element on the sketch. This indicator will use the SmartSnap highlighting