Learning Basic Commands to Get Started - AutoCAD 2011 and AutoCAD LT 2011: No Experience Required - page 67

4. Your command line now reads Specify first fence point: . Using
the Fence method, you will draw an imaginary line through the objects
you want to trim. Use your cursor to draw a line that crosses the two
horizontal lines across the opening somewhere between the cutting
edge lines (see Figure 2.34).
Specify next fence point or
Lines to be trimmed
FiGuRE 2.34 Lines selected to be trimmed
NOTE Note that in these trimming procedures, the endpoints of the
cutting edge lines, as well as the lines themselves, are used as cutting edges.
The opening is trimmed away (see Figure 2.35).
FiGuRE 2.35 Lines are trimmed to make the opening.