Halliday & Matthiessen (2014: 3,4):
… (1) focus on the text as an object in its own right; (2) focus on the text as an instrument for finding out about something else. Focusing on text as an object, a grammarian will be asking questions such as: Why does the text mean what it does (to me, or to anyone else)? Why is it valued as it is? Focusing on the text as instrument, the grammarian will be asking what the text reveals about the system of the language in which it is spoken or written. … But the text has a different status in each case: either viewed as artefact, or else viewed as specimen. … specimen here might mean specimen of a particular functional variety, or register …