Martin (1992: 211-2):
The final reformulation option to be noted has to do with the summative generalisation realised through in short, in brief, in summary, to sum up and so on. This relation ranges retrospectively across an accumulation of more specific meanings which are brought together by way of summary.
REFORMULATION:REWORK:GENERALITY:GLOBAL[4:122] The riot began shows that riot is a process term, even though it is in nominal form. Similarly, the violence ended suddenly marks violence as a process term even though it has no corresponding verb form. [cf 'violate']
In short, several colligations in the text show that many nominals are encoding actions, not things.
In SFL theory, this conjunctive relation is classified as summative clarification, a type of elaboration (see Halliday & Matthiessen 2004: 542). Here it has been relocated to similarity — i.e. comparison, a type of enhancement.