code: def _slicespec2boundsspec(slicespec,scs):
          
          r1,r2,c1,c2 = slicespec
  
          left,bottom = scs.matrix2sheet(r2,c1)
          right, top  = scs.matrix2sheet(r1,c2)
  
          return ((left,bottom),(right,top))
docs: Convert an iterable slicespec (supplying r1,r2,c1,c2 of a
          Slice) into a BoundingRegion specification.
  
          Exact inverse of _boundsspec2slicespec().