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Build accessible, headless UI components with modern architecture patterns. Use when creating component libraries, design systems, or reusable UI primitives. Handles compound components, state management, accessibility, styling hooks, and API design. Includes HTML (controllers, ReactiveElement) and React (hooks, context) patterns. Triggers: "create component", "component pattern", "compound component", "headless component".

Component Architecture Patterns

Build accessible, headless UI components using proven patterns from Base UI, Radix, and Ark UI. These patterns are framework-agnostic — core concepts apply across React, Vue, Svelte, Solid, and vanilla JS.

Primary sources:

• Base UI Handbook
• Ark UI — Cross-framework implementation
• Zag.js — State machines for UI components

Framework-specific: react.md | html.md

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Core Principles

1. Headless over styled — Separate behavior from presentation
2. Compound over monolithic — Small composable parts over config-heavy megacomponents
3. Controlled + uncontrolled — Support both state ownership models
4. Accessible by default — ARIA, keyboard nav, focus management built-in
5. State via attributes — Expose state through data-* for framework-agnostic styling

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Pattern 1: Compound Components

What: Components as related parts sharing state through context, each mapping 1:1 to DOM elements.

Why:

• Declarative — assemble like building blocks, reorder/omit parts freely
• Each part is an independent styling target
• DOM structure maps directly to ARIA roles

Standard hierarchies:

Type	Parts
Popups	Root → Trigger → Portal → Positioner → Popup → Arrow
Collections	Root → List → Trigger + Panel
Forms	Root → Label → Control → Description → Error

Ref: Base UI Composition

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Pattern 2: Controlled & Uncontrolled State

What: Support external state control OR internal state with consistent prop naming.

Why:

• Flexibility for simple and complex use cases
• Predictable API across components
• Change details enable fine-grained control (cancel changes, track reasons)

Convention:

State	Uncontrolled	Controlled	Handler
Open	defaultOpen	open	onOpenChange(open, details)
Value	defaultValue	value	onValueChange(value, details)
Checked	defaultChecked	checked	onCheckedChange(checked, details)

Change details: { reason, event, cancel() }

Ref: Base UI Customization

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Pattern 3: Prop Getters

What: Functions returning HTML attributes for DOM elements, abstracting logic from rendering.

Why:

• Portable across frameworks (React, Vue, Svelte, Solid)
• Clean separation of concerns
• Composable via mergeProps()

Example: getTriggerProps() returns { aria-expanded, aria-haspopup, onClick, onKeyDown }

Ref: Zag.js, Downshift

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Pattern 4: State via Data Attributes

What: Expose state through data-* attributes for CSS targeting.

Why:

• Framework-agnostic styling
• No JS needed for state-based styles
• Inspectable in DevTools

Standard attributes:

• data-open / data-closed — Visibility
• data-checked / data-unchecked — Toggle state
• data-highlighted — Focus within group
• data-disabled, data-valid, data-invalid
• data-side, data-align — Positioning

CSS variables: --available-height, --anchor-width, --transform-origin

Ref: Base UI Styling

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Pattern 5: Accessibility

What: ARIA, keyboard navigation, focus management built into architecture.

Why:

• Accessibility is structural, not decorative
• Users expect standard keyboard interactions
• Consistent patterns reduce errors

Key concerns:

• ARIA attributes — Auto-managed from state
• Focus trapping — Modals trap focus within
• Roving tabindex — One tabbable item, arrows navigate
• Virtual focus — aria-activedescendant for long lists
• Typeahead — A-Z jumps to matches

Ref: Base UI Accessibility, WAI-ARIA Practices

For detailed accessibility patterns, load the aria skill.

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Pattern 6: Floating Positioning

What: Position popups relative to triggers with collision detection.

Why: Handles viewport boundaries, scroll, resize automatically.

Config: side, align, sideOffset, collision (flip/shift), trackAnchor

Ref: Floating UI

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API Conventions

Category	Props
Interaction	disabled, required, readOnly
Collections	multiple, loopFocus, orientation
Popups	modal, closeOnEscape, closeOnOutsideClick, keepMounted
Positioning	side, align, sideOffset, collision

Imperative actions: actionsRef exposing open(), close(), toggle()

See props.md for naming conventions.

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Reference Files

File	Contents
html.md	HTML controllers, mixins, context
videojs-element.md	ReactiveElement lifecycle, properties, controllers
react.md	React hooks, context, refs
props.md	Prop naming, conventions, defaults
styling.md	Data attributes, CSS variables
animation.md	CSS transitions, JS animation libs
polymorphism.md	render vs asChild patterns
collection.md	Collections, portals, virtualization
anti-patterns.md	Common component mistakes
videojs.md	Video.js component architecture

For accessibility patterns (ARIA, keyboard, focus), load the aria skill.

Review

For structured component reviews, load the review workflow:

File	Contents
workflow.md	Review process and severity
checklist.md	Component review checklist
templates.md	Issue and report formats

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Implementation Sources

Resource	Use For
Base UI Source	React reference implementations
Radix Primitives	Alternative approach
Zag.js	Framework-agnostic state machines
Floating UI	Positioning

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Related Skills

Need	Use
Accessibility patterns	aria skill
API design principles	api skill
Documentation patterns	docs skill
Component API reference	api-reference skill