Halliday & Matthiessen (1999: 225):
There are other “transphenomenal” motifs, often related to these [fractal types], which are more specific in their scope; for example the foregrounding of perceptual space, and of the concrete having extension in space, so that these serve as models for construing more abstract, non-spatial realms; and more specifically, the spatial construction of the human body as an orientational framework.