Halliday & Matthiessen (1999: 204):
Those of the elaborating type may function in the nominal group either as Thing or as Facet. As Facet (always constructed with of), they serve to construe the element functioning as Thing in some particular guise or perspective; for example, picture in this will give you a general picture of the situation, kind in a jet cat is a kind of passenger vessel, example in there were no examples of successful integration. As Thing, they are participants in their own right, either ‘objects’ (e.g. is that picture for sale) or ‘abstractions’ (e.g. Darwin showed how species first evolved).