Halliday & Matthiessen (1999: 212):
This relation is typically typically a temporal or spatial one involving the thing as a discoursal instance rather than the thing as a general experiential class. Consequently, like qualities of extension, qualities of enhancement tend to serve as deictic elements (Post-Deictic) rather than as Epithets; as Post-Deictics, they come before Numeratives in the structure of the nominal group: the preceding / subsequent two meetings. Here they relate a specific referent, recoverable in the current situation: the subsequent two meetings : the two meetings that followed this one. But the spatial qualities can also, being taxonomic, serve to subclassify the thing they are assigned to: interior monologue, external pipes. Here they relate to a general class of thing, inferable from the experiential system: interior monologue : monologue that is within a person, external pipes : pipes that are outside a house.