“It was a dark and stormy night; the rain fell in torrents, except at occasional intervals, when it was checked by a violent gust of wind which swept up the streets (for it is in London that our scene lies), rattling along the housetops, and fiercely agitating the scanty flame of the lamps that struggled against the darkness.” ― Edward Bulwer-Lytton
In this, I maybe thought except at occasional intervals seemed like maybe an adverbial phrase maybe placing information on how it fell. Maybe it doesn't seem to place information on how it falls, it may place information on how it may not fall. So then I guess I thought maybe it seemed like a parenthetical? May except at occasional intervals seem like an adverbial phrase, parenthetical phrase, or maybe something different?