The adjoining profiles are simply overlapped by 100 mm or so, with the upper section inside the lower one. This prevents any water draining out of the joint allowing it to be carried down to the eaves.

Where there is a sprocket or change of angle in the verge, the end of lower section is cut to be perpendicular to the angle of the upper section allowing the upper section to fit inside without distortion. Click for more information on the DV7.