Halliday & Matthiessen (1999: 144-5):
One participant elaborates another one along the dimensions of delicacy, realisation, or instantiation. In other words, the elaboration sets up a relationship either of generality (delicacy), of abstraction (realisation), or of token to type (instantiation): see Table 4(4). There is another variable whereby elaboration involves either identity or membership along the dimension in question.
