WCAG

WCAG (Web Content Accessibility Guidelines, published by the W3C) is the numbered rulebook the whole accessibility world points at. It is organized under four principles, POUR: perceivable, operable, understandable, robust. Under those sit numbered success criteria, each graded A, AA, or AAA. When a contract, an RFP, or a lawsuit says 'accessible', it almost always means level AA. WCAG 2.2 is the current W3C Recommendation, and it is the one that added target size, focus appearance, and accessible authentication. Read the paperwork before you assume it, though: plenty of laws, contracts, and procurement policies still name 2.1 or even 2.0 outright, and the version they name is the version you owe.

Criteria are cited by number, and knowing a handful makes docs and audit reports readable: 1.1.1 non-text content (alt text), 1.4.1 use of color, 1.4.3 contrast minimum (4.5:1 for body text), 2.1.1 keyboard, 2.4.7 focus visible, 2.5.8 target size minimum, 3.3.1 error identification, 4.1.2 name, role, value. The 'Understanding' document for each criterion is the useful read, not the terse criterion text itself.

The big misconception: passing an automated scan is not passing WCAG. Tools like axe or Lighthouse catch roughly a third of the criteria, mostly the mechanical ones (missing alt, bad contrast, unlabeled inputs). Whether the alt text is meaningful, whether focus order makes sense, whether the error message actually explains the error: all human judgment. A green Lighthouse score with a keyboard trap in the checkout modal is still a broken site.