CORNER allows you to specify that when using the POLYLIN, 
NGON options, the radius is measured from a vertex (corner)
of the polygon.

Indicate the center position of the polygon, using a 
Position Menu option.

In 2-D construction mode, the center point is projected to 
the current construction plane, and the polygon is created
in the construction plane.

In 3-D construction mode, the polygon is created in the
plane that is parallel to the construction plane and
passes through the indicated center position.
