Halliday & Matthiessen (1999: 466):
For example, if we recognise figures of saying (usually overlooked as a distinct type), this goes together with certain other features: with the distinction between phenomena and metaphenomena, and between ideas and sayings, with the organisation of projections as sequences rather than as figures, with the identification of symbol sources as a kind of participant, and with the recognition of circumstances of matter. In other words, we have to consider syndromes of features that occupy a region of semantic space.