(I) Interface

The Interface phase focuses on user experience, visual design, and how users interact with your system. This includes design systems, accessibility, internationalization, and mobile/PWA patterns.

Why Interface Matters

Good interface design:

• Improves usability - Users can accomplish tasks easily
• Increases accessibility - Works for everyone
• Enhances brand - Consistent, professional appearance
• Reduces support - Intuitive interfaces need less help

Key Interface Decisions

1. Design Systems

When to use:

• Multiple products/teams
• Consistency required
• Scalable component library
• Design-to-code workflow

Components:

• Design tokens (colors, spacing, typography)
• Component library
• Documentation
• Patterns and guidelines

Relevant Content:

• Design Systems - Complete design system guide
• Design Tokens - Token architecture
• Component API Design - Good component APIs
• Theming Architecture - Multi-theme support
• Responsive Design Tokens - Responsive system
• Dark Mode Implementation - Dark mode patterns
• Typography System - Type scale
• Spacing System - Spacing scale

Decision Framework:

Use Design System if:
✅ Multiple products/teams
✅ Consistency required
✅ Scalable component library
✅ Design-to-code workflow

Start Small:
1. Design tokens
2. Basic components (Button, Input)
3. Documentation
4. Expand gradually

2. Accessibility

When to prioritize:

• Legal requirements (ADA, Section 508)
• Public-facing applications
• Government contracts
• Inclusive design goals

Key Areas:

• Screen reader support
• Keyboard navigation
• Color contrast
• Focus management
• ARIA patterns

Relevant Content:

• Accessibility Patterns - Complete accessibility guide
• Screen Reader Testing - NVDA, JAWS, VoiceOver
• ARIA Live Regions - Dynamic announcements
• Focus Management SPA - SPA focus patterns
• Keyboard Shortcuts - Custom shortcuts
• Accessible Animations - Motion accessibility
• Color Contrast Systems - WCAG AAA compliance
• Accessible Forms Advanced - Complex forms

Decision Framework:

WCAG Level A:
✅ Basic accessibility
✅ Semantic HTML
✅ Alt text

WCAG Level AA:
✅ Color contrast 4.5:1
✅ Keyboard navigation
✅ Screen reader support
✅ Most common target

WCAG Level AAA:
✅ Color contrast 7:1
✅ Sign language
✅ Extended audio
✅ Highest compliance

3. Internationalization (i18n)

When to implement:

• Multiple languages
• Global audience
• RTL languages (Arabic, Hebrew)
• Locale-specific formatting

Key Areas:

• Translation management
• RTL support
• Date/time formatting
• Number/currency formatting
• Pluralization

Relevant Content:

• Internationalization Architecture - i18n structure
• RTL Support - Right-to-left languages
• Date/Time Handling - Locale formatting
• Number Formatting - Currency, units
• Pluralization Rules - Complex plurals
• Lazy Loading Translations - Code splitting
• Translation Fallback - Missing keys
• Internationalization Overview - Complete guide

Decision Framework:

Basic i18n:
✅ Translation files
✅ Language switcher
✅ Basic formatting

Advanced i18n:
✅ RTL support
✅ Complex pluralization
✅ Locale-specific formatting
✅ Lazy loading translations
✅ Translation fallback

4. Mobile and PWA

When to prioritize:

• Mobile-first audience
• Offline requirements
• App-like experience
• Push notifications

Key Areas:

• Service workers
• Offline-first architecture
• App shell pattern
• Install prompts
• Network-aware components

Relevant Content:

• Mobile and PWA - Mobile patterns overview
• Service Worker Strategies - Caching strategies
• Background Sync - Sync when online
• Push Notifications - Web Push API
• App Shell Architecture - Shell pattern
• Offline-First Architecture - Offline patterns
• Install Prompt Strategies - A2HS optimization
• Network-Aware Components - Adapt to network
• Performance Mobile - Mobile optimization

Decision Framework:

Basic Mobile:
✅ Responsive design
✅ Touch-friendly
✅ Mobile-optimized

PWA:
✅ Service worker
✅ Offline support
✅ Install prompt
✅ Push notifications
✅ App shell

5. Form Patterns

When to optimize:

• Complex multi-step forms
• Validation requirements
• Accessibility needs
• User experience critical

Key Areas:

• Form validation
• Error handling
• Accessibility
• Multi-step forms
• Conditional fields

Relevant Content:

• Accessible Forms Advanced - Complex forms
• Error Handling Advanced - Error patterns

Decision Framework:

Simple Forms:
✅ Basic validation
✅ Inline errors
✅ Submit on enter

Complex Forms:
✅ Multi-step
✅ Conditional fields
✅ Advanced validation
✅ Accessibility
✅ Error recovery

6. List and Data Display

When to optimize:

• Large datasets
• Performance critical
• Smooth scrolling
• Virtual scrolling

Key Areas:

• Virtual scrolling
• Infinite scroll
• List animations
• Performance optimization

Relevant Content:

• List Architecture - List patterns
• Windowing Virtualization - Virtual scrolling
• Infinite Scroll Observer - Infinite scroll
• List Animation Performance - Smooth animations
• FLIP Animations - List animations
• Deep Object Memoization - Performance

Decision Framework:

Small Lists (< 100 items):
✅ Render all
✅ Simple pagination

Large Lists (100+ items):
✅ Virtual scrolling
✅ Infinite scroll
✅ Performance optimization

Interface Checklist

Use this checklist when designing interface:

Design System

• Design tokens defined
• Component library planned
• Documentation strategy
• Theming requirements
• Dark mode needed?

Accessibility

• WCAG level determined
• Screen reader testing
• Keyboard navigation
• Color contrast checked
• Focus management
• ARIA patterns

Internationalization

• Languages identified
• RTL support needed?
• Date/time formats
• Number/currency formats
• Pluralization rules
• Translation strategy

Mobile/PWA

• Mobile-first design
• Service worker strategy
• Offline support
• Install prompt
• Push notifications
• Network-aware components

Forms

• Form validation
• Error handling
• Accessibility
• Multi-step support
• Conditional fields

Lists

• Virtual scrolling needed?
• Infinite scroll
• Performance optimization
• Animation strategy

Common Patterns

Simple App

Interface:
- Basic design system
- WCAG AA
- Single language
- Responsive design
- Simple forms

Medium App

Interface:
- Full design system
- WCAG AA
- 2-5 languages
- PWA capabilities
- Complex forms
- Virtual scrolling

Complex App

Interface:
- Enterprise design system
- WCAG AAA
- 10+ languages, RTL
- Advanced PWA
- Multi-step forms
- Advanced list patterns

Trade-offs

Design System

Pros:

• Consistency
• Faster development
• Better UX
• Scalability

Cons:

• Initial investment
• Maintenance overhead
• Learning curve
• Can be restrictive

Accessibility

Pros:

• Legal compliance
• Better UX for all
• SEO benefits
• Inclusive design

Cons:

• Development time
• Testing complexity
• May limit design

Internationalization

Pros:

• Global reach
• Better UX
• Market expansion

Cons:

• Development complexity
• Translation costs
• Testing overhead
• RTL complexity

PWA

Pros:

• Offline support
• App-like experience
• Push notifications
• Installable

Cons:

• Service worker complexity
• Cache management
• Browser support
• Testing complexity

Next Steps

After designing interface, move to:

• Optimizations (O) - Improve performance and reliability

Remember: Great interfaces are invisible—users focus on their tasks, not the interface itself.