I want to cut away something of a part in an assembly. So, I select a face of the part, Start 2D Sketch, and draw a rectangle, which I want to use as the shape to cut into my part. I want to control the position of this rectangle precisely. So, I select the Dimension tool and first click on one side of my rectangle. Then I try to click on an edge of a neighboring part in my assemply, because the cut rectangle needs to be a certain distance from this edge. However, I cannot make this edge - or any other edges in my assembly - active/light up/be selectable, instead the Dimension tool always gives me the length of the side of the rectangle I selected. I can extrude said rectangle and cut away from the part, but how can I control the precise location of this cut?