/// <summary>
 /// Adds an ObjRef to the list.
 /// </summary>
 /// <param name="objref">An ObjRef to add.</param>
 public void Add(Rhino.DocObjects.ObjRef objref)
 {
     if (null != objref)
     {
         IntPtr pConstObjRef = objref.ConstPointer();
         IntPtr pThis        = NonConstPointer();
         UnsafeNativeMethods.ON_ClassArrayCRhinoObjRef_Append(pThis, pConstObjRef);
     }
 }