What this is

A <button> brings a tab stop, Enter and Space activation, and a role announcement for free. A <div onClick> brings none of them, and generated UI code reaches for the div because the styling starts from zero. The rest of this family is the same story: semantics deleted for visual convenience.

Why it matters

For keyboard and screen reader users these are not polish, they are the interface. A control that cannot be tabbed to does not exist. A deleted focus outline turns the page dark for anyone navigating without a mouse. A skipped heading level reads as a missing section to someone skimming by structure.

What the probe looks for

Click handlers on non-interactive elements with no role and no keyboard path. tabIndex above zero. Heading levels that jump. outline: none with no visible replacement.

What the probe does not do

Landmarks, alt text, form labels and skip links are owned by the A11y Landmarks probe. Color contrast needs rendered pixels. Focus management in modals and route changes is behavior, and belongs to a running-page check, not a source scan.