Definition of "adverbially"

Here the use is not part of a predication but does not seem to be merely adverbially subordinate.

1991, Frances Austin, “Points of English Syntax 1968-1983”, in Ingrid Tieken-Boon van Ostade, John Frankis, N. E. Osselton, editors, Language usage and description: studies presented to N.E. Osselton ..., page 182