Comment Adjuncts “express the speaker’s attitude either to the proposition as a whole or to the particular speech function” (H & M, p.129).
1) Propositional (ideational) type – occur only with declarative clauses and, as with mood Adjuncts, may appear in the thematic, neutral or afterthought positions. Propositional type comment Adjuncts are located “according to their significance for the textual organisation of the clause…[and] are strongly associated with the boundary between information units” (H & M, p.129). The difference between these and circumstances of manner can often be difficult for learners (compare: wisely, he didn’t act with he didn’t act wisely).
2) Speech functional (interpersonal) type – may occur with either declarative clauses, which express the speaker’s angle (Frankly, I was surprised.), or with interrogative, which express the listener’s angle (Frankly, were you surprised?). They are more likely to be restricted to initial or final position. This type also falls into two sub-types: qualified, which can be followed by speaking as in generally speaking, and unqualified, which cannot be followed by speaking.
The comment Adjunct network and examples can be found here.