Halliday & Matthiessen (1999: 145):
Elaborating figures can thus be used to construe hyponymic taxonomies. In other words, they are, among other things, a theory of the systemic organisation of the meaning potential itself; and, by virtue of this fact, they can be used to elaborate it further. For example:
The fuels of the body are carbohydrates, fats and proteins. These are taken In the diet. They are found mainly In cereal grains, vegetable oils, meat, fish and dairy products. Carbohydrates are the principal source of energy in most diets. […] Fats make up the second largest source of energy in most diets. […]