Halliday (2008: 167):
Those nominalised processes and qualities, which are semantic junctions of the core meaning of their original categories, as verb or adjective, with the core meaning of their adopted category as a noun, are the semiotic analogue of a written clause or sentence, which is a flow of meaning that has been frozen into a text; and the verbalised relators, likewise a semantic junction of their original category as conjunction with the core meaning of their adopted category as a verb, are analogous to the punctuation devices that link one written chunk with another.