Focus Rail

Purpose

A continuous secondary rail that promotes one collection item into a readable primary surface — a primary/secondary reading pattern, not a tab bar.

Good for

• Chapter indexes, project collections and focused archives
• A small set where one item deserves more reading room than the rest

Avoid for

• Utility navigation or large database filters
• Independent items that do not share a primary reading context

How many items

Three to eight; a continuous rail should stay scannable.

Mobile

The rail becomes a horizontally scrollable, touch-sized selector above the primary surface.

Motion intensity

Low. Only the selected surface animates; the rail itself uses ordinary flow and never creates a scroll trap.

Accessibility

• Rail entries are native buttons with pressed and current state.
• Arrow, Home and End keys move through the rail.
• The primary surface has a polite live region and does not require hover.

Composes with

Split Narrative for a two-plane story instead of a rail-plus-surface; Gallery ↔ List Morph when the primary surface itself should change shape.