Comment Adjuncts […] As far as position in the clause is concerned, these are like Conjunctive Adjuncts: they tend to occur thematically, finally, between Theme and Rheme, or between Mood and Residue; and when medial, they are typically associated with a boundary between information units. Although they are interpersonal rather than textual in function, expressing the speaker’s comment on what he is saying, they are not themselves part of the proposition, and therefore fall outside the Mood-Residue structure.
- Halliday (1985), a pag.83