Halliday & Matthiessen (1999: 81):
As well as being figures in their own right, such configurations can also be used as qualifications of a class of participant, such as cat — as figures serving to qualify that category with respect to its own rôle in the figure. Here the figure is being viewed in a participant perspective; this is achieved by downranking the figure so that it acquires the status of a property. Grammatically, this perspective would be realised in the nominal group as a Qualifier of some Thing …