CARRIER FUNCTIONALITIES - Reference points

With thanks to the community which is pointing us in the right direction, we
have been working to transform our static carriers into dynamic ones -
following the Top Gun example. Looking at the reference_points.cfg it seems
clear that: attachpt_cable_X_Y are the attachpoint for cable X, with Y=1 being
the port position and Y=2 being the starboard position. These generate working
cable and work fine (except a graphical issue that I will highight in a
separate question). Could you please clarifiy what are the function and
position of: attachpt_runway_start attachpt_runway_end attachpt_runway_edge