Together these flags define a cell orientation. If 'kSwapMask'
is true, then canonical traversal order is flipped around the
diagonal (i.e. i and j are swapped with each other). If
'kInvertMask' is true, then the traversal order is rotated by 180
degrees (i.e. the bits of i and j are inverted, or equivalently,
the axis directions are reversed).
Together these flags define a cell orientation. If 'kSwapMask' is true, then canonical traversal order is flipped around the diagonal (i.e. i and j are swapped with each other). If 'kInvertMask' is true, then the traversal order is rotated by 180 degrees (i.e. the bits of i and j are inverted, or equivalently, the axis directions are reversed).