[vtkusers] How to -- save vtkProperty data to an XML file?

[kent williams]

We already save instance of vtkPolyData to XML files.  We already add
data to the vtkFieldData for vtkPolyDataInstances to save object names
and other information in the XML file with the PolyData.

What I'd like to do is also save the state of an associated
vtkProperty in the same XML file with the PolyData.  I know I could
laboriously go through and add every attribute of vtkProperty to the
Field Data.

I also know I could use get the vtkXMLMaterial and find a way to save
its contents as a string and add the string to vtkFieldData.

What I don't know is if there is a 'right' way to do this or at least
a not too difficult way to do it.