Halliday & Matthiessen (2014: 568):
It is the secondary group, or last secondary group if there is more than one, that realises the process type of the clause, e.g. [material:] she seemed to mend it, [behavioural:] she seemed to laugh, [mental:] she seemed to like him, [verbal:] she seemed to tell us, [relational:] she seemed to be nice.