In DEX you can add graphical curves. In schematics they have no electrical significance. However, in PCBs they have significance if they are placed on electrical layers such as the top or bottom layer; here they will leave copper traces and will provide an electrical connection to everything that is connected to them.
Curves have a width that can be zero for an infinitely thin curve. However if you add curves to a PCB, you need to make sure their width is at least the size of the manufacturing minimum width.
Curves also have color and can be semi-transparent. It is even possible to define an invisible curve. If you have snap to objects enabled, objects will snap to invisible curves.
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Closed
Closed with Border and Filled
Closed with No Border and Filled