Is there a name for this structure: one linear spine with optional sideways branches, like a crossword, not a tree
So I've been working on a project and I keep running into this question. The structure I'm thinking about doesn't quite fit the usual IF categories and I'm wondering if this community has a term for it or knows of examples.
The idea: one main narrative thread, linear, top to bottom. But from any node you can branch sideways. The branches don't change where the main story goes, they're more like optional depth. Another character's version of that exact moment. A hidden memory. Extra context for readers who want to look. The main story always keeps moving forward, the branches are explorations off the spine.
The closest analogy I have is a crossword. The main word reads down. Intersecting words read across. Every cell has exactly one place. Its not a tree, theres no forking path where you end up somewhere different. Its one story, with optional layers.
This feels different to me from classic CYOA or Twine-style branching where choices affect outcome. Here the reader doesn't change the story, they just choose how deep to go into each moment. Feels closer to something like annotations? But written as actual scenes, not notes.
I keep thinking about a mystery novel where the main thread follows the detective, and sideways at every scene you have the killer's private thoughts. Same moment, both heads. You can read straight through and get the full story, or you can stop and go sideways whenever you want.
The other things I'm thinking about for this format: co-authorship where different writers own different branches inside the same work. Paywalled branches, so the core story is accessible but deeper layers are optional paid content. And post-publication expansions, new branches added after the main work is already out, like DLC basically.
I'm a software developer building something around this idea and honestly not sure if its a new format or just a weird implementation of something that already has a name. Does this exist somewhere in the IF world and I just missed it?
What would you call this structure? And have you seen it done anywhere?