SEP 43: Distinguish types, classes, tags in collections

Currently (2023-04-17), the code in the build script that produces ‘Collections’ flattens the hierarchy of types, tags, and classes.

A document of type: references ends up in collections["references"] in the same way that a document with tags: references would. By convention I don’t use type or class names as tags, but this is not yet enforced.

Ultimately I want for it to be possible to reference and emit collections of arbitrary specificity. To that end I envision the below format:

  style: title
    - backups

This would emit a collection containing:

This is an excessively complicated example collection for illustrative purposes and would not be common, but the flexibility and expressiveness of this approach is what I’m interested in.