Extend Frame
This window is used to extend frames. To perform an extension, you need to select a boundary object to extend the frame to. The boundary object can be another frame or a shell. If a frame is used as the boundary object, the program treats it as an infinite line.

1. Select boundary object
Toggling this button on allows you to pick a boundary object. Once selected, the program will automatically switch to selecting the frame to be extended.
2. Select frame to extend
Toggling this button on allows you to pick the frame to extend. Click near the end of the frame in the direction you want it to extend.
3. Close button
Closes the window and ends the frame extension command.