Halliday & Matthiessen (2014: 586):
Fig. 8-14 Projecting verbal group/clause nexuses:
(a) Mary wanted to go (i) as verbal group complex [preferred], (ii) as clause complex;
(b) Mary wanted John to go (i) as verbal group complex, (ii) [preferred] as clause nexus
Halliday & Matthiessen (2014: 588):
A verbal group nexus is intermediate between a clause nexus and a verbal group: a verbal group construes a single event, and a clause nexus construes two distinct processes; but a verbal group nexus construes a single process consisting of two events. These different options are available to speakers and writers when they construe their experience of the flow of events. They choose whether they construe a given experience as a process consisting of a single event, as a process consisting of a chain of two (or more) events, or as a chain of two (or more) processes.