Any text in spoken English is organized into what may be called 'information units'. (...) this is not determined (...) by constituent structure. Rat… - Michael Halliday

[... language, as an example of a semiotic system, contains all four levels of organization as follows:] First, it is transmitted physically, by sound waves traveling through the air; secondly, it is produced and received biologically, by the human brain and its associated organs of speech and hearing; thirdly it is exchanged socially, in contexts set up and defined by the social structure; and fourthly it is organized semiotically as a system of meanings

Foregrounding, as I understand it, is prominence that is motivated

The theme is what is being talked about, the point of departure for the clause as message, and the speaker has within certain limits the option of selecting any element in the clause as thematic.