Halliday & Matthiessen (2014: 170):
Because a systemic account of grammar takes paradigmatic organisation as fundamental, there is no problem with incorporating considerations of tone (or intonation, in general) into the account since terms in systems may realised by different syntagmatic patterns such as fragments of constituency-like structure, e.g. ‘declarative’ ↘ Subject ^ Finite or prosodic patterns, e.g. ‘reserved statement’ ↘ tone 4.