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();
//At 2.x - CompositeHVDatumTransformation xml_compositehv =
//      CompositeHVDatumTransformation.CreateFromXML(xml);

var xml_compositehv = CompositeHVDatumTransformation.CreateFromXml(xml);

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