Halliday & Matthiessen (2004: 594):
On the one hand, expansion is manifested in the augmentation of the clause by circumstances: these circumstantial augmentations cover all three types of expansion, with enhancement being the most highly developed one. On the other hand, expansion is manifested in the relation of a ‘relational’ clause: ‘intensive’ clauses embody elaboration, ‘possessive’ clauses extension, and ‘circumstantial’ clauses enhancement. In the domain of the nominal group, there are also various manifestations of the three types of expansion. Thus the Qualifier may elaborate, extend or enhance the Thing…