I think you’ll find the term ‘focus’ is used in phonology for the name of a system information focus, whose features are realised by relations between the Tonic function and lexicogrammar. (More hill than ditch ;-) Focus isn’t used as a function term.
I think you’ll also find that Jim has always been fastidiously careful about distinguishing terms between strata, which I guess he learnt from Michael (all those years ago), and has been teaching others, as the canon has proliferated (all these years since).He is also fastidiously careful about acknowledging those whose work he and colleagues are building on. How to show respect for others is nicely modelled in current work on register systems, carefully framed in relation to that of Halliday (53 refs), Hasan (42), Carmel Cloran, Cate Poynton and others...
… the system of INFORMATION. This is a system not of the clause, but of a separate grammatical unit, the information unit (cf. Halliday, 1967a, 1967/8; Halliday & Greaves, 2008: Section 5.1). The information unit is a unit that is parallel to the clause and the other units belonging to the same rank scale as the clause.
The misunderstanding of INFORMATION as phonology can be sourced to Martin (1992: 384, 401).
[2] This is misleading, because it is untrue. To be clear, 'focus' refers to the lexicogrammatical element of structure that is realised by tonic prominence (Halliday & Matthiessen 2014: 116). Halliday (1992: 371):
… confusion invited by the use of grammatical terminology for semantic description in several SFL publications, particularly those dealing with grammatical metaphor (e.g. Halliday and Matthiessen, 1999).
But, in any case, the objection is based on a misunderstanding. A functional grammar interprets grammatical form in terms of its function, which is to realise meaning. In grammatical metaphor, the meaning of a grammatical form is incongruent with the meaning being realised. It is the use of meaning terminology on both strata that enables the systematic description of grammatical metaphor. And, as Halliday & Matthiessen (1999: 237) point out:
Of course, what we are recognising here as two distinct constructions, the semantic and the grammatical, never had or could have had any existence the one prior to the other; they are our analytic representation of the overall semioticising of experience — how experience is construed into meaning. If the congruent form had been the only form of construal, we would probably not have needed to think of semantics and grammar as two separate strata: they would be merely two facets of the content plane, interpreted on the one hand as function and on the other as form.
[5] For the motivation behind this theological term for what in science would be called 'the standard theory', see The Culture Of 'Faith' In The SFL Community.
[6] This misleads through what it omits. It is true that Martin generally acknowledges his sources, though he doesn't always acknowledge that an idea comes from his source rather than himself. Evidence here. But more importantly, having acknowledged his sources, Martin then renames their ideas so that all future references will be to his work and not theirs, thereby giving himself credit for the ideas of others. See for example, here (Martin 1992) and here (Ngo, Hood, Martin, Painter, Smith & Zappavigna 2022).
[7] To be clear, Martin named these scholars because they provided the source of his ideas. Martin then rebranded 'register' as his stratum of context, so all references to register by his readership refer to his model rather than Halliday's original model. Moreover, Martin's model of register is full of self-contradictions. For example, his register is context, not language, despite register being a functional variety of language (cf. beef and dairy cattle not being categorised as 'cattle'); and though it is context, not language, it is instantiated as text, which is language, not context. And this is just the tip of the iceberg.
