Martin (1992: 350):
The meronymy option has been chosen where available in the analysis presented above; this means that the action strings are oriented towards activity sequences in the field, with actions taken as steps in activity sequences. This bias is balanced in part by the interpretation of processes as delicate experiential subclasses of clause in lexicogrammar.
 The actions and activity sequences are analyses of the meanings made in the text. They model the semantics of language, not the ideational dimension of context.
 In SFL theory, clause is the rank of grammatical form at which the functional choice of PROCESS TYPE (along with AGENCY) becomes available, provided the entry condition major is met.