“This thesis presents a model which accounts for variations in typographic form in terms of four underlying sources of structure. The first three relate to the three parts of the writer-text-reader relationship: topic structure, representing the expressive intentions of the writer; artefact structure, resulting from the physical constraints of the medium; and access structure, anticipating the needs of the self-organized reader. Few texts exhibit such structures in pure form. Instead, they are evidenced in typographic genres—ordinary language categories such as ‘leaflet’, ‘magazine’, ‘manual’, and so on – which may be defined in terms of their normal (or historical) combination of topic, access and artefact structure.” (Rob Waller PhD. Thesis 1987) – courtesy of karel van der waarde