Export polyline as ...
This option allows you to export a set of polylines to the DXF format, to be read for example in AutoCAD. When selecting this function, you are asked to select the output filename. After that, you are asked to provide the decimal precision that the polyline's points should have.
You can specify a distinct output filename and decimal precision for each polyline. Otherwise, in the select file dialog you can check Do not ask again and you will set the decimal precision only once for all the polylines. The filename will be also assigned automatically.