Halliday & Matthiessen (2014: 392):
The complex functional entity formed by the conflation of Head and Thing acts as the fulcrum of the nominal group: before it, as Premodifier, a sequence of words having distinct experiential functions; after it, as Postmodifier, one or more embedded items which may be prepositional phrase or non-finite or finite clause.The Premodifier can then be interpreted in logical terms as a hypotactic word complex.