Confusing Formal Constituency And Function Structure

Martin, Matthiessen & Painter (2010: 164-5):

Further, multivariate structures are all modelled as constituency structures – as configurations of component parts of a unit whole (see IFG2 Section 2.1, IFG3 Section 1.1.3 on grammatical constituency).

There are thus two basic types of grammatical structure whose characteristics are summarised in Table 5.4.

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[1] This is potentially misleading. On the one hand, Halliday & Matthiessen (2004: 384, 383) explain:

Although we have modelled all multivariate structures in terms of constituency, this structural mode is in fact most appropriate for the experiential mode of meaning. That is, the relationships among the elements in a multivariate structure can be characterised as segmental from an experiential point of view but as prosodic from an interpersonal point of view and as culminative from a textual one. 

But, on the other hand, it confuses formal constituency (as set out in IFG2 Section 2.1 and IFG3 Section 1.1.3) with function structures. To explain, formal constituency is modelled as the grammatical rank scale, such that clauses consist of groups and phrases, which consist of words, which consist of morphemes. In contrast, the function structure of a rank unit, such as clause, is the relation between the structural elements, each of which is the function of a clause constituent, group or phrase (this being more precisely the case for experiential structures than the others, as suggested above).

[2] Trivially, contrary to Table 5.4, nominal and verbal groups have multivariate as well as univariate structure.