Ideas for future improvements

### Overview
This is a collection of ideas for future improvements. Some of these depend on web platform features that are not yet widely supported, so they are gathered here for tracking rather than filed as individual issues.
### Ideas

#### Ordering:
- [ ] **`reading-flow` CSS property:** Once the [`reading-flow`](https://developer.mozilla.org/en-US/docs/Web/CSS/reading-flow) CSS property has wider browser support beyond Chrome, add it as a reference to the Reading Order annotations.
- [ ] **tab roving reference:** Add a link to the [Roving tabindex](https://nik.digital/posts/tab-roving) pattern as a resource in the Ordering documentation.

#### System Feedback:
- [ ] **Live Regions: ARIA Notify API:** Once the [ARIA Notify API](https://github.com/nicolo-ribaudo/tc39-proposal-aria-notify) is available, consider adding stamps and labels for it. These could be prepped ahead of availability.

Start by reviewing the existing Reading Order and System Feedback documentation or annotation entry points; this issue names no files or tests. Check the linked reading-flow, roving tabindex, and ARIA Notify resources and confirm their availability before adding the applicable references, stamps, or labels.

索引モデルが issue の本文から書いたものです。