Halliday & Matthiessen (1999: 612):
Children gradually build up an inventory of such proto-signs, and towards the end of the first year the signs begin to form systems, sets of contrasting terms in particular proto-semantic domains or micro-functions: typically, the instrumental (e.g. 'I want/1 don't want'), regulatory (e.g. Do that!/ Do that!!'), interactional (e.g. I’m here/ where are you?'), and personal domains (e.g. 'I like that/ I'm curious about that').