All vertices in face are aligned and project to xzplane from its best fit plane for the 2d offset operation then converted back therefore resulting offset holes are always planar.
Extude faces doesn’t work well with non-planar faces (with holes or with trigulate applied)
21/11/2012 added check on original face planarity

require offsetFace.mll
faceOffsetByColorCmd(float minValue, float Value, int planarCheck)