Rail
Rail is a scrollbar that maps authorship. Its track shows who wrote each part of a document and flags what needs you. It moves only while the model writes below the fold.
Scroll the lease, or drag the rail. Tap “Model: draft the next section” and watch the new section stream in on the track.
Anatomy
When to use
- Long documents written by people and the model together: leases, reports, minutes.
- Any scrolling region where people need to find what needs their decision.
- Not for short content that fits on one screen.
Behaviour
| Segment | Means |
|---|---|
| Ink | A person wrote it |
| Still pigment | The model wrote it and a person accepted it |
| Flowing pigment | The model wrote it and it awaits review |
| Ochre dot | A decision is needed here |
| Glowing segment | The model is writing it now |
Wheel, touch and keyboard scrolling stay native. The rail adds a map; it never replaces the scroll.
Best practices
- Never scroll the reader to new text. Show the pill and let them choose.
- Flag a section only when it needs a person, and say why in the section itself.
- Keep the rail beside the content on every screen size; it is narrow enough for phones.
Accessibility
- The rail is hidden from screen readers; the document itself carries the same information in words.
- The document is focusable and scrolls with the keyboard.
- Flags are dots and words, so they don’t depend on colour.
Specifications
- Width
- 14 px rail, 3 px inset track
- Minimum segment
- Proportional to the section’s height
- Motion
- Only the segment being written flows
- Thumb
- 1.5 px lapis outline, 9% lapis fill