Basically, relative adverbs modify their antecedent and antecedents should be nouns, which I learned.
However, in the following sentence, 'where', which I think is a relative adverb, seems to modify 'outdoor,' which is an adverb:
Visual awareness is also heightened outside, where the eyes are exercised by motion.
Also, if 'where' is relative adverb, then it is used as a nonrestrictive relative adverb. Does 'where' modify 'outdoor,' despite the fact that it is an adverb, or is its antecedent the whole sentence before the comma? Or isn't 'where' a relative adverb at all?