Extrusion length of the trimming curve:

When trimming by sweeping curve is done in "Extrusion" mode, the  >>  button allows to define the extrusion length of the curve on both side of its position.

The red arrow indicates the direction of the first extrusion length.

When you validate a value written in a cell with the [tab] key, a preview of the extrusion is displayed. This allows you to check if the values are suitable.

Once the values defined, validate this option with the  OK  button.