Halliday & Matthiessen (2014: 192-3):
The speech functional type also falls into two sub-types, qualified and unqualified. The qualified type is closely related to projection; they can be expanded by ~ speaking as in generally speaking, and if construed as a separate intonation unit they will typically take tone 4 [fall-rise]. The unqualified type, which cannot be followed by ~ speaking, are either claims of veracity (if separate, then tone 4) or signals of assurance or admission (if separate, then tone 1 [fall]; the clause is then typically tone 1 if assurance, tone 4 if admission).