One of the methods of defining a cut line is using the edges of either the surfaces selected for milling, or of some other surfaces (specified using the Tool Extent or the Alternate Surfaces option).
When you define a cut line From Edges, the CHAIN menu appears, providing the following methods of edge selection:
One By One—Select individual edges from the specified surfaces.
Tangnt Chain—Select a chain of tangent edges by selecting an edge that is a part of a tangent chain. The edge must belong to the specified surfaces.
Bndry Chain—Select boundaries of the specified surfaces. When you choose this option, the whole boundary of the specified surfaces highlights in cyan. The CHAIN OPT menu appears with the following options:
Select All—Include all the highlighted edges.
From-To—Select a start vertex (curve end), then an end vertex (curve end). One of the chains connecting these vertices highlights. Specify which chain you want to include using the Next and Accept options.
Surf Chain—Select a chain of edges that belong to the same surface. You will be prompted to select a surface, and then specify which edges to include using either the Select All or From-To options in the CHAIN OPT menu.
Intent Chain—Select an edge. Based on this selection and the design intent criteria, the system selects a chain of edges.
The Unselect option in the CHAIN menu allows you to cancel the previous set of selections.