Use this option to sketch a Bézier curve snapped to a surface or solid. A single Bézier curve can be sketched to snap across multiple faces of a solid, but to only a single surface.
To sketch a Snapped Bézier curve:
If you attempt to sketch outside the selected surface, the curve is snapped to the edge, as shown below:
You can edit the Bézier curve in the normal way, but you cannot move a point to a position outside the surface.