POUR: the four principles every audit checks

What axe, Lighthouse, and WCAG actually test

WCAG 2.2 organizes accessibility into four principles. Every audit tool maps its checks to one of them:

• Perceivable — users can perceive the content. Includes alt text, captions, color contrast, focus visibility, text resize.
• Operable — users can operate the interface. Keyboard accessible, no keyboard traps, generous touch targets, no flashing >3×/sec.
• Understandable — users understand the content. Predictable navigation, clear errors, consistent labels.
• Robust — works with current AND future assistive tech. Valid HTML, proper ARIA, name/role/value on every interactive element.

Why memorize these four

When axe reports "color-contrast" violation, you'll know it's a Perceivable issue → check contrast ratios. When it says "no keyboard handler" → Operable. The category tells you what to fix, fast.

The one rule that beats them all

Use the right native element. A real <button> is keyboard-operable, focus-visible, screen-reader-announced, and high-contrast by default — passing all four principles for free. A <div> with click handlers fails all four until you ARIA-patch each one separately.

This module's structure

We'll spend lessons 2-11 on the most common violations you'll hit in practice (focus, contrast, motion, ARIA-live). Lesson 12 is a real before/after page: take a "looks fine" landing page and fix every a11y issue we plant in it.