Martin (1992: 211):
Within the "identifying" mode, both relational clauses and internal conjunction make a distinction between "exhaustive" and "exemplificatory" (i.e. non-exhaustive) manifestation. In this respect [4:115] contrasts with [4:120].
[4:115] The riot began shows that riot is a process term, even though it is in nominal form.
That is, the fact that riot is a noun does not mean that it cannot represent an action as its colligation with began shows.
REFORMULATION:REWORK:ABSTRACTION:EXEMPLIFY[4:120] When a clause shows that an idea encoded as a noun has a temporal beginning and end, this stands as evidence that the "idea" is an action.
For example, certain of these occur as Mediums with verbs indicating they have a beginning and end, which concepts apply only to actions.
In SFL theory, the opposition in conjunctive relations here is between two main types of apposition within elaboration: expository ('that is') and exemplifying ('for example'). Here Martin has relocated them at several degrees of delicacy within similarity — i.e. comparison, a type of enhancement.