You can use this option to limit the following:
Use the following technique to limit objects:
Keep original
Cutting object deselected/selected.
Cutting object unlocked/locked.
Create and use polygon as cutter.
Create and use composite curve as cutter.
Keep both.
Trim both.
Next solution.
Limit selection flyout. Repeatedly clicking on this button cycles through the following limit selection modes:
Limit selection.
Project along the axis normal to the principal plane.
Project along the axis normal to the view.
Project along surface normal.
Limit surface to a curve.