Martin (1992: 214-5):
Where similar lines of argumentation and interpretation are for some reason separated from each other, then the conjunction again is used to pick up the thread as it were. Again is one of two conjunctions in English that regularly connects non-adjacent material in text (the other is still …). Text [4:116] is repeated below and then elaborated in such a way as to separate the two arguments compared in [4:128] in order to illustrate the function of this "resumptive" again.
COMPARISON:CONTINGUOUS [sic][4:116] 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.
COMPARISON:INTERRUPTED[4:128] The riot began shows that riot is a process term, even though it is in nominal form. It is a general fact… . Actions can be… . Such incongruence… .Again the violence ended suddenly marks violence as a process term even though it has no corresponding verb form.
 The words again and still are not conjunctions; they are adverbs that frequently function interpersonally, as modal Adjuncts. Of the two, still can also serve as a conjunctive Adjunct, typically marking a conjunctive relation of concessive condition (Halliday & Matthiessen 2004: 127, 543).
 In SFL theory, resumptive conjunctive relations are a type of clarification, which is a type of elaboration. It is typically marked by as I was saying, to resume, to get back to the point and so on. Here it is misconstrued as a type of comparison, which is misconstrued as a type of similarity, within comparative relations (misconstrued as internal), which in SFL theory, is a type of enhancement.