Disjunct adverbials are words and phrases that provide additional information to frame an entire clause. Disjunct adverbials denote the attitude of the speaker toward or judgment of the proposition such as truthfulness of manner of speaking.
Disjunct adverbial is a grammatical function.
The grammatical forms that can function as the disjunct adverbial in English grammar are the adverb phrase, prepositional phrase, and adverb clause.
Disjunct adverbials are not constituents of either the subject or the predicate.
Brinton, Laurel J. & Donna M. Brinton. 2010. The linguistic structure of Modern English, 2nd edn. Amsterdam: John Benjamins Publishing Company.