Attempts to determine "holes" in the mesh by chaining naked edges together.
Then it triangulates the closed polygons adds the faces to the mesh.
RhinoCommon (in RhinoCommon.dll)
Public Function FillHoles As Boolean
true if successful, false otherwise.
This function does not differentiate between inner and outer naked edges.
If you need that, it would be better to use Mesh.FillHole.