Allows you to pick curves-on-surface.
Curves-on-surface are special curves that exist on surfaces. They are used to mark out which parts of a surface to trim.
Usually, you create curves-on-surface by intersecting or projecting other geometry onto a surface. You do not usually need to edit curves-on-surface by hand.
To pick a curve-on-surface, choose Pick > Object Types > Curve on Surface and click the curve-on-surface.