references/act.md

ACT conformance — how this engine scores against a corpus it did not write

The recall matrix in this repository proves that each rule fires on the defect written FOR it. That is circular. The W3C ACT-Rules Community Group publishes rules with passed / failed / inapplicable examples authored independently of this project, so running the engine over them measures something a self-authored fixture cannot.

How to read this. An ACT example asserts something about ITS OWN rule and nothing else, so each case is judged only with the engine rules mapped to that ACT rule — never with the whole engine. Only normative findings count (an advisory recommendation never flips a criterion, so it cannot fail a case either). Rules needing a rendered page or a human call are declared, not scored — saying so beats quietly scoring zero.

Summary

Partially consistent is the ACT Rules Format's own term for a tool that never reports a false positive but does not catch everything — it is a coverage statement, not an error. Divergent means every deviation on that rule is listed below with the argument for it.

Scored rules

Notes and documented divergences

• Letter spacing in style attributes is not !important — definite below-threshold author-important values; computed-unit cases remain rendered
• Visible label is part of accessible name · reports on Passed Example 6: an icon FONT renders the text 'search' as a glyph, so the visible label is not the text in the DOM — a fact only the rendered page carries
• Audio or video element that plays automatically has a control mechanism · reports on Inapplicable Example 2: the source cannot tell that the referenced media has no audio track
• Audio or video element that plays automatically has a control mechanism · reports on Passed Example 3: the pause mechanism is a custom button wired in JavaScript, not a native controls attribute
• ARIA state or property is permitted — covers the name-prohibited roles; the full per-role permitted-attribute matrix is not encoded
• Element with aria-hidden has no content in sequential focus navigation · reports on Passed Example 4: a focus-sentinel link inside an aria-hidden wrapper: it IS reachable by Tab, and only a runtime focus handler bounces it back — the same call axe-core makes
• Line height in style attributes is not !important — definite below-threshold author-important values; computed-unit cases remain rendered
• SVG element with explicit role has non-empty accessible name — role=img on <svg> is handled by the same rule
• Audio or video element avoids automatically playing audio · reports on Inapplicable Example 2: the source cannot tell that the referenced media file is silent
• Audio or video element avoids automatically playing audio · reports on Passed Example 3: the pause mechanism is a custom button wired in JavaScript, not a native controls attribute
• Audio or video element avoids automatically playing audio · reports on Passed Example 2: a #t= media fragment shortening playback below 3s is not resolvable from source
• Word spacing in style attributes is not !important — definite below-threshold author-important values; computed-unit cases remain rendered
• Meta element has no refresh delay (no exception) — this variant drops the >20h exception the engine honours, so long delays are knowingly not reported
• Iframe element has non-empty accessible name · reports on Inapplicable Example 3: a tabindex=-1 iframe is still exposed to assistive tech and still needs a title (RGAA 2.1 requires one unconditionally)
• Table header cell has assigned cells — only the explicit headers-wired shape is decided; scope-based assignment needs a full table model
• Element with lang attribute has valid language tag · reports on Inapplicable Example 2: lang="" on an element carrying text declares no language for that text; ACT deems the rule inapplicable, this engine reports it under 3.1.2
• Form field has non-empty accessible name — placeholder-as-label is deliberately NOT mapped: a placeholder does contribute to the accessible name, so ACT passes it — ultra11y still reports it, as a stricter house rule under 3.3.2.
• Video element auditory content has captions — presence of a caption track; whether the captions are accurate is a judgment call

Declared gaps — statically decidable, not implemented yet

Out of the static engine's reach — routed, not ignored

The corpus is vendored at scripts/vendor/act-testcases.json (refreshed by pnpm run build:act:refresh, and daily by the act-refresh workflow) so the suite stays offline and deterministic. ACT-Rules Community Group test cases are © their contributors under the W3C Software and Document License — see NOTICE.