Halliday & Matthiessen (2014: 609):
The clause complex thus provides the resources for realising logico-semantic relations grammatically as tactic patterns. This is the most extensive domain of grammatical structure. However, in the semantic organisation of text, logico-semantic relations extend beyond the semantic sequences that are realised by clause complexes; they extend to rhetorical paragraphs and even to whole texts. The semantic organisation of text in terms of logico-semantic relations is brought out by different forms of analysis, including the conjunctive reticular analysis developed by Martin (e.g. 1992: Chapter 4) drawing on the work by the Hartford stratificationalists and the rhetorical-relational analysis based on the framework of Rhetorical Structure Theory (RST) developed by Mann, Matthiessen & Thompson (e.g. 1992).
To be clear, Martin's (1992) conjunction, now relabelled connexion, is a confusion of two grammatical systems — Halliday & Hasan's (1976) original cohesive system of conjunction (textual metafunction) and Hallidays (1985) structural system of clause complexing (logical metafunction) — rebranded as discourse semantics, wherein the expansion categories are misunderstood and misapplied and the category of projection is entirely absent. Evidence here.