[abenedik]

DumpHierarchy is defined as an extension method for Model3D (in Ab3d namespace).
So to use it, the code that is executing should have "using Ab3d" or and other namespace under Ab3d defined.

You can also use the longer way to get the dump string (in c#):
string infoText = Ab3d.Utilities.Dumper.GetObjectHierarchyString(model3D);
System.Diagnostics.Debug.WriteLine(infoText);