Interpolate

Interpolate - to introduce (something additional or extraneous) between other things or parts; interject; interpose; intercalate.

This seems like an important term for literature. It’s been used to describe passages in which a character in one part of a story, takes over the narration of another part - the “twice-told tale.”

But at a more fundamental level it could refer to anything that is interjected into “pure” narrative - extraneous information, perspective (of which the twice-told tale is an example), footnotes (e.g., David Foster Wallace, RIP), flashbacks, flashforwards. The purpose in all these cases, of course, is to build or revise meaning in the story.
October 7
Imagism