public static CompositeHVDatumTransformation CreateFromXml( 
   string xmlString
)

{
  HVDatumTransformation hv1 = HVDatumTransformation.Create(108034);
  HVDatumTransformation hv2 = HVDatumTransformation.Create(108033, false);
  List<HVDatumTransformation> hvs = new List<HVDatumTransformation>() { hv1, hv2 };

  // create from enumeration
  CompositeHVDatumTransformation compositehv =
                  CompositeHVDatumTransformation.Create(hvs);
  int count = compositehv.Count;      // count = 2

  List<HVDatumTransformation> transforms =
                 compositehv.Transformations as List<HVDatumTransformation>;
  HVDatumTransformation tranform = transforms[0];
  // transform.Wkid = 108034

  // get inverse
  CompositeHVDatumTransformation inverse_compositehv =
         compositehv.GetInverse() as CompositeHVDatumTransformation;

  // create from xml
  string xml = compositehv.ToXml();

  var xml_compositehv = CompositeHVDatumTransformation.CreateFromXml(xml);

  // create from json
  string json = compositehv.ToJson();
  CompositeHVDatumTransformation json_compositehv =
      DatumTransformation.CreateFromJson(json) as CompositeHVDatumTransformation;
}