The literary term excursus has to do with a more neutral sort of digression. An idea is expanded upon mostly in the appendix or the footnotes. Maybe the subject discussed will be of interest to only certain readers and maybe the information will benefit those readers who are more interested in back story. If you are familiar with Herman Melville’s Moby Dick, you will find that the novel makes extensive references to whaling, a kind of excursus in its own right,
Some instances of the word in literature:
“You are sure that I would not be well advised to make certain excisions and eliminations? You do not think it would be a good thing to cut, to prune? I might, for example, delete the rather exhaustive excursus into the family life of the early Assyrians?”
― The Inimitable Jeeves“But there is another class of assassinations, which has prevailed from an early period of the seventeenth century, that really does surprise me; I mean the assassination of philosophers. For, gentlemen, it is a fact, that every philosopher of eminence for the two last centuries has either been murdered, or, at the least, been very near it; insomuch, that if a man calls himself a philosopher, and never had his life attempted, rest assured there is nothing in him; and against Locke’s philosophy in particular, I think it an unanswerable objection (if we needed any), that, although he carried his throat about with him in this world for seventy-two years, no man ever condescended to cut it. As these cases of philosophers are not much known, and are generally good and well composed in their circumstances, I shall here read an excursus on that subject, chiefly by way of showing my own learning.”
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The word obstreperous comes from ob– which means in the way plus strepere, a verb that means to make a noise or to rebel against something. So the adjective works well especially with unruly children, politicians, rebel groups and certain kinds of families.