one is an "off_grid" DRC type, which can be used to check geometry
that is below the manufacturing grid. Normally magic prevents the
grid from being subdivided below the manufacturing grid, but this
limit can be removed and replaced by DRC checks to check for such
errors in a GDS file of unknown origin. The second version looks
for interactions between subcells that end up with intersections
of non-manhattan geometry landing on points that are not on the
database internal grid. Such errors cannot be seen by magic's DRC
engine by definition, and so must be detected while flattening
geometry for the DRC checks.
Tim Edwards