Tabs

mandatory

Horizontal navigation within a single context — primary tabs (top of content) and secondary tabs (filter within tab). Material parity (`/components/tabs`). Includes scrollable tabs, swipe gesture, and accessibility contract.

Spec — Tabs

Facet *isual*do Koder Design. Material parity: https://m3.material.io/components/tabs.

2 tab levels

Level	Position	Use
rimary	Top of content area, beneath app bar	Main view switcher (Profile / Activity / Settings)
econdary	Within a primary tab's content	Filter within view (All / Mine / Shared)

Maximum 2 levels — never nest a 3rd. If needed, use sub-navigation (drawer, menu) at the deeper level.

Anatomy (primary tab row)

┌────────────────────────────────────────────┐
│   Profile     Activity    Settings         │   ← labels
│   ━━━━━━━                                  │   ← indicator (active)
└────────────────────────────────────────────┘

*ontainer* full width, surface bg
*abel* title-small (14/20, weight 600)
*ndicator* 2 px line below active tab, accent color
*adding per tab* 16 px horizontal, 12 px vertical
*eight* 48 px

R1 — Tab content options

Mode	Content
Label only	Just text
Icon + Label	18 px icon above OR before label
Icon only	Single 24 px icon (with `aria-label`)
Label + count	"Inbox (12)" — count as badge or inline

Don't mix modes within a single tab row. All tabs in a row use the same mode.

R2 — States

State	Label color	Indicator
Inactive (rest)	`text-muted`	—
Inactive + hover	`text`	—
Inactive + focused	`text` + focus ring	—
Active (current)	`accent`	`accent` line (2 px)
Active + focused	`accent` + focus ring	`accent` line
Disabled	38% opacity	—

R3 — Indicator animation

When user clicks a different tab:

Indicator slides from old position to new (motion-medium, ~250ms)
Color of active label transitions from text-muted → accent
Content area cross~~fades to new content (motion~~fast)
Reduced motion: indicator snaps; no fade

R4 — Fixed vs scrollable tabs

Mode	When	Behavior
ixed	Total tabs fit within container width	Equal-width tabs OR centered with auto sizing
crollable	Tabs overflow container	Horizontal scroll, no fixed width, indicator scrolls with tabs

Switch automatically per layout: at Compact class scroll if more than 4 tabs; at Expanded class fixed up to 6 tabs.

R5 — Swipe gesture

On touch surfaces:

Swipe left/right within content area switches to adjacent tab
Swipe matches indicator motion (1:1 with finger)
Release with > 50% threshold: switches; < 50%: snaps back
Indicator animates smoothly with swipe

Disabled when content has its own horizontal scroll (e.g., carousel).

R6 — Tab content area

Content area renders below tab row
Switching tabs: cross~~fade (motion~~fast) OR slide~~in (motion~~medium)
— pick one style per app; don't mix
Preserve scroll position per tab (going back to "Profile" tab
remembers its scroll)
Lazy-render content on first visit; keep mounted after

R7 — Secondary tabs

Look slightly different from primary to indicate hierarchy:

Aspect	Primary	Secondary
Container	Same as toolbar	Same as surrounding content
Indicator	2 px solid below	2 px or chip-style border
Padding	16 px horizontal	12 px horizontal
Label weight	600	500

Secondary tabs render WITHIN a primary tab's content area, not in the app bar.

R8 — Accessibility

role="tablist" on container
role="tab" on each tab; aria-selected="true" on active
aria-controls pointing to the panel id
Panel: role="tabpanel" + aria-labelledby pointing to tab id
Keyboard:
- Arrow Left/Right cycles tabs (wrap around at ends)
- HomeEnd jumps to firstlast
- Tab moves OUT of tab row into the panel
Screen reader announces: "Tab, Activity, 2 of 3, selected"

R9 — Per-preset variation

Preset	Indicator
`material3`	2 px solid line at bottom
`material2`	3 px solid line at bottom
`ios_cupertino`	Active tab has `accent-tint` bg (no line)
`gnome`	Active tab background tint + 1 px line
`windows_11`	Mica backdrop on row, accent line
`brutalist`	4 px thick line + sharp corners
`terminal_classic`	ASCII underline `[==Active==]`

R10 — Forbidden patterns

❌ More than 2 levels of tabs (use drawer/menu for deeper nav)
❌ Tab labels longer than 20 chars (truncate or use shorter)
❌ Hiding inactive tabs (defeats the "all options visible" purpose)
❌ Confirmation dialog on tab switch (defeats quick navigation)
❌ Tabs that navigate to different URLs (use links, not tabs —
tabs are within ONE context)

Cross-link

interaction/states.kmd — focus/hover visuals
themes/color-roles.kmd — accent indicator
themes/motion.kmd — indicator slide animation
foundations/elements.kmd — Control family