Halliday & Matthiessen (1999: 126-7):
The limiting case is that where what is being expanded is not a figure but an element of a figure, in which case instead of a sequence of figures we get a sequence of elements, realised by group or phrase complexes. Thus instead of Schank conceived of scripts and Abelson conceived of scripts as a solution to this problem, a sequence of figures where there are two processes of conception, we get Schank and Abelson conceived of scripts as a solution to this problem, a single figure with a sequence of elements (serving as Senser of a single process). Putting this in terms of the grammar, the sequential relationships remain constant, but the rank at which the complex occurs depends on the domain being related: see Figure 3-11.
