The FBD editor enables you to insert an object on an existing line and automatically connect it to the line. This feature is available for all objects having one input pin and one output pin, such as variable boxes, contacts and coils. This feature is mainly useful when entering pieces of Ladder Diagrams. Just draw a horizontal line between left and right power rails: this is the rung. Then you can simply insert contacts and coils on the line to build the LD rung.