[A register is constituted by] the linguistic features which are typically associated with a configuration of situational features - with particular … - Michael Halliday

Traditionally, grammar has always been a grammar of written language: and it has always been a product grammar" ['Product' is here used as one term of the Hjelmslevian pair process/product.] A process/product distinction is a relevant one for linguists because it corresponds to that between our experience of speech and our experience of writing: writing exists whereas speech happens.

Language... is a range of possibilities, and an open end set of options in behavior that are available to the individual in his existence as social man. The context of culture is the environment of any particular selection that is made within them... The context of culture defines the potential, the range of possibilities that are open. The actual choice among these possibilities takes place within a given context of situation.

A physical system is just that: a physical system. What is systematized is matter itself, and the processes in which the system is realized are also material. But a biological system is more complex: it is both biological and physical — it is matter with the added component of life; and a social system is more complex still: it is physical, and biological, with the added component of social order, or value. … A semiotic system is still one step further in complexity: it is physical, and biological, and social —and also semiotic: what is being systematized is meaning. In evolutionary terms, it is a system of the fourth order of complexity