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Field tip: for testing html accessibility, test both the ordinary path and the first case that makes your assumptions false.
Source-reading note: the exact semantics here come from the HTML element/attribute you chose, not its CSS appearance.
When this goes wrong, the browser usually keeps rendering. That is what makes the bug easy to miss: recovery can hide a broken source document. In this lesson, the focus is manual and automated accessibility checks. That matters because HTML is interpreted by a parser and then exposed to browser features such as navigation, accessibility tooling, form controls, media handling, and script APIs. A correct-looking screenshot can still hide a poor document model.
<main><h1>Checkout</h1><form>...</form></main>
Start with the smallest meaningful example. The working snippet demonstrates the core syntax, but the important part is what each piece contributes: the element supplies semantics or behavior, attributes refine that meaning, and surrounding structure gives the browser context. Don't add markup just because a framework or copied example happens to include it.
Don't confuse browser-side convenience with a security boundary. The markup in testing html accessibility should improve behavior, but authoritative validation and policy belong at the trust boundary that processes the request.
<button type="button" aria-expanded="false" aria-controls="filters">Filters</button><section id="filters" hidden>...</section>
Now put the same idea under pressure. A realistic failure is: Combine keyboard testing, screen-reader checks, browser accessibility trees, and automated audits. The browser may recover, ignore an invalid combination, or leave the user with a control that appears visually fine but behaves differently than expected. That is why source inspection and keyboard testing belong in the workflow.
<img src="chart.png"alt="Orders increased from 120 in May to 190 in June.">
For this topic, the edge case is worth remembering: HTML has legacy parsing and compatibility behavior, so invalid markup does not always fail loudly. If you are debugging a strange result, reduce the page to one element at a time, validate the source, and inspect the resulting DOM. Small reproductions beat guessing at the full application.
Keep the markup close to the meaning of the content. Future CSS and JavaScript changes then have a stable surface to work against.
Engineering judgment: prefer the native HTML behavior described here before reaching for a custom widget.
Finish the lesson once you have worked through the material. This awards ★ 20 XP.