Doc for Vector3d.RotateAbout: 
left-handed rotation

Spline3d.IntersectSplineWithPlane (Cf: Misc3d).

Vector3d.NearestPair, Vector3d.NearestTriple (Cf: Misc3d)

Doc in Matrix3d and Vector3d: the coordinate system is left handed, i.e., positive x to the right, positive y up and positive z 
into the screen.  Rotations are right handed (i.e., if your right thumb points in the direction of the axis of rotation, your right 
fingers will curl in the direction of the rotation).