# Feature: Tabs Runtime

## Intent

Problem: tab styling alone does not synchronize selected tab, panel visibility, keyboard focus, and ARIA state.
Users or stakeholders: application teams, QA, keyboard users, screen reader users, and framework package maintainers.
Desired outcome: implement accessible Tabs behavior with progressive enhancement over existing `.sui-*` markup.
Non-goals: implement routing, persistence, or application-specific lazy loading.

## Scope

In scope: tab selection, roving tabindex, panel visibility, disabled tabs, ARIA state, activation mode, events, and cleanup.
Out of scope: CSS layout, animations, remote data loading, and URL synchronization.

## Markup Hooks

- Root: `[data-sui-tabs]` or `[data-sui-component="tabs"]`.
- Tablist: `[role="tablist"]` or `[data-sui-tabs-list]`.
- Tab: `[role="tab"]` or `[data-sui-tab]` with `data-sui-target` or `aria-controls`.
- Panel: `[role="tabpanel"]` or `[data-sui-tab-panel]`.
- Value: optional `data-sui-value`.

## Behavior

1. Runtime initializes only when tabs hooks are present.
2. Selection dispatches `sui:tabs:before-change`; cancellation blocks selection.
3. Successful selection dispatches `sui:tabs:change`.
4. Arrow keys move focus among enabled tabs using roving tabindex.
5. Activation can follow focus or require Enter/Space, based on options.
6. Selected state updates `aria-selected`, `tabindex`, hidden panels, and `data-sui-state`.
7. Cleanup removes listeners and restores no application state outside the component.

## Accessibility

Align with WAI-ARIA Tabs guidance. Preserve native buttons or links where provided and avoid replacing semantic markup.

## Acceptance Examples

Scenario: arrow navigation
Given three enabled tabs
When ArrowRight is pressed on the first tab
Then focus moves to the second tab without leaving the tablist.

Scenario: panel synchronization
Given a tab controls a panel
When the tab is selected
Then only its panel is exposed to assistive technologies.