Here is pertinent part of the official spec:
http://www.ldraw.org/article/512.html#overlaps
Specifically, it says:
http://www.ldraw.org/article/512.html#overlaps
Specifically, it says:
Quote:Every effort must be made to remove overlapping co-planar polygons (line type 3 or 4). Where overlapping polygons are unavoidable, the overlap must be kept to the absolute minimum.