The additive [Accompaniment] represents the process as two instances; here both entities clearly share the same participant function, but one of them is presented circumstantially for purposes of contrast. We could say 'Fred and Tom both came'; but 'Fred came as well as Tom' distinguishes the two as regards their news value (ʻnot only Tom but also Fred cameʼ).
- Halliday (1985), Pag. 141