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Robust is the fourth WCAG principle: your content must work reliably across browsers, devices, and assistive technologies.

Tools change over time. Robust markup keeps working with today's screen readers and the ones people will use tomorrow.

Browsers and assistive tech parse your markup. Valid HTML with closed tags and unique IDs gives them a clean tree to read. ✅

Every control needs a name, role, and value that tech can read. A real checkbox exposes all three to a screen reader automatically.

A real button already has the right role and value. Reaching for a native element is the easiest path to robust markup.

When HTML cannot express a role, ARIA can add it. Use it sparingly to give custom widgets a name, role, and state.

A wrong role can make a control announce nonsense. The first rule of ARIA: no ARIA is better than bad ARIA.

Labels and ARIA link elements by id. A duplicate id breaks those links, so screen readers point at the wrong thing.

The only way to know it is robust is to try it. Test with a real screen reader and keyboard, not just your own eyes.

If your page only works because one browser is forgiving, it is fragile. Standard, valid code survives the next update.

Ask of every component: will assistive tech read its name, role, and value correctly? If you are unsure, your markup is not yet robust.

Let us test the Robust principle.

You learned that Robust means your code works across tech: valid HTML, native elements, careful ARIA, unique IDs, and real testing. POUR complete! 🚀