Halliday & Matthiessen (2014: 260):
Thus, static location in space [enhancement] is construed relationally – she’s in the dining room, but dynamic motion through space is construed materially – she’s walking into the dining room. Similarly, static possession [extension] is construed relationally – she has a mahogany dining table, but dynamic transfer of possession is construed materially – she’s getting a mahogany dining table; she’s being given a mahogany dining table; and static quality [elaboration] is construed relationally – the bottle’s empty, but dynamic change in quality is construed materially – the bottle’s emptying; she’s emptying the bottle.