Wrapping and tacking a 3/8 inch thick flat bar around the perimeter of the riser to act as both a stiffener and a safety device, lest someone should ever fall onto the edge of the riser. The angle is being used to keep the flat bat flat with the plane of the lid: when doing this kind of wrapping it is very easy to let things go haywire, quickly, if one is not vigilant, especially when going around corners.

Photo by Rick Brigger