aria-valid-attr
aria-* attributes must be real, defined ARIA attributes
Checks that every aria-* attribute name present in the DOM is a real attribute defined by the WAI-ARIA specification.
Applies to. Applies to any element in the composed DOM that carries at least one attribute whose name starts with "aria-".
Expectation. Each aria-* attribute name is a real attribute defined by the WAI-ARIA specification (catches typos / made-up attribute names, which are silently ignored by assistive technology and therefore a real, deterministic defect). Reported at CANTTELL rather than FAIL: an aria-* attribute the spec does not define is inert, so nothing about the element's exposed name, role or value changes because it is there. Where the author meant a real attribute and the element ends up without a name, that absence is the naming rules' decision, not this one's. ACT 5f99a7 maps 1.3.1/4.1.2 as secondary requirements, "less strict" than the rule itself.
Examples
<button aria-label="Save">Save</button>
`aria-label` is a real, defined ARIA attribute.
<button aria-labeledby="x">Save</button>
`aria-labeledby` is a typo (the real attribute is `aria-labelledby`) and is silently ignored by assistive technology.