Returns or sets the splitting side .
The splitting side is the side of the splitting element
kept after the split.
A positive side refers to the same orientation
than the splitting element normal vector.
Example:
The following example returns in sptSide the splitting side
of the split shape mySplit, and then sets it to
catPositiveSide:
Set sptSide = mySplit.SplittingSide
mySplit.SplittingSide = catPositiveSide