Halliday & Matthiessen (1999: 354):
…text and context are construed together. There is an important variable here, of course, that we have already referred to as the cline from 'language in reflection' to 'language in action'. In situations of the 'language in action' kind, where the discourse is a relatively minor component of the total activity, the grammar and semantics are obviously less constructive of the whole than in a 'reflection' context such as the present one.