Halliday & Matthiessen (2014: 550):
In spoken English, the sequence of clauses within a clause complex may be mapped onto one or more information units; that is, there are textually different ways in which a clause complex can be mapped onto an information unit complex. The unmarked mapping is one (ranking) clause = one information unit. Thus the paratactic sequence 1 ^ 2 and the hypotactic sequence β ^ α would each be chunked into two information units (realised by different tone sequences, tone 3 followed by tone 1, and tone 4 followed by tone 1, respectively). However, there are regular departures from this unmarked pattern.(1) When the dependent clause in a hypotactic nexus is included within the dominant clause, the nexus may be chunked into three information units, with three points of New information (as in //4 John //4 who arrived late //1 missed the speeches //).
(2) When the dependent clause follows its dominant clause in a hypotactic nexus (progressive sequence), it may be included in the same information unit as the dominant clause, with the focus of New information within the dependent clause (as in //1 I came because he told me //).
(3) When the logico-semantic relation of the nexus is one of projection, the projecting clause may be part of the same information unit as the projected clause, being tonally cliticised to it.