feat(checks/label): support ARIA element internals properties - #5170

…als (#5182)

## Summary

Form-associated custom elements (`static formAssociated = true` +
`attachInternals()`) can be labeled with native `<label>` elements,
which the browser exposes through `ElementInternals.labels`. axe-core's
accessible-name computation dropped these labels entirely, because:

1. `nativeTextAlternative` builds its naming methods from the element
spec, and `getElementSpec()` returns `{}` for custom element names — so
`labelText` was never invoked for a custom element.
2. Label resolution in `labelText` only looked at the DOM by `id`
(`label[for]`) / ancestor wrapping.

This wires up the [proposal's final
step](https://github.com/dequelabs/ocarina-team/blob/main/proposals/axe-core/element-internals.md#supporting-formassociated-elements-with-labels).

## Changes

- **`native-text-alternative.js`** — `findTextMethods` detects a
form-associated custom element via `ElementInternals` and appends
`labelText`.
- **`label-text.js`** — `labelText` reads `internals.labels` directly
when present (the authoritative, complete set of explicit + implicit
labels), falling back to the existing DOM resolution otherwise.

`ElementInternals.labels` throws `NotSupportedError` on a custom element
that isn't form-associated, so both reads are guarded with try/catch.
Both paths are gated by the existing `elementInternals` run option —
with the flag off, `vNode.elementInternals` is `undefined` and behavior
is unchanged.

### Why `internals.labels` (not the DOM lookup)?

It's the browser-authoritative association and is the *complete* set —
it already includes the ancestor-wrapping label. Routing it through the
existing explicit + implicit merge would count a wrapping label twice,
so `labelText` uses the internals list exclusively when present.

## Out of scope

- **`checks/label` (`explicit`/`implicit`)** — no change needed. They
resolve labels via `label[for=id]` / `closest('label')`, which already
cover custom elements, and the `label` rule selector is `input,
textarea` anyway. Matches the proposal ("rules that look at
implicit/explicit labels will not need to be updated") and #5170 leaving
those checks untouched.
- **Non-labelable custom elements with a stray `<label for>`** —
labelable-ness/role territory (#5039), pre-existing.
- `getResolvedRefs` (#5151) — native `<label>`/`for` association isn't
an ARIA idref, so it doesn't apply here.

## Testing

- `test/testutils.js` — new shared `testutils-form-element`
(form-associated).
- `label-text.js` — explicit, implicit, multiple, implicit+explicit
dedup, global-map protocol, non-form-associated fall-through, Shadow
DOM.
- `native-text-alternative.js` — explicit/implicit pickup, gating
(non-form-associated gets no label), flag-off no-op.

No integration test added — this is a `commons/text` change with no
rule/check edits; the nearest rule impact (`aria-input-field-name` on a
role-bearing custom element) depends on role-via-internals selection
(#5039), which isn't wired yet.

Closes #5045

All notable changes to this project will be documented in this file. See
[commit-and-tag-version](https://github.com/absolute-version/commit-and-tag-version)
for commit guidelines.

##
[4.13.0](v4.12.1...v4.13.0)
(2026-08-05)

### Features

- **aria-actions:** add aria-actions to allowed ARIA attributes
([#5200](#5200))
([029655d](029655d)),
closes [#4584](#4584)
[#5199](#5199), references
[#5215](#5215)
[#5215](#5215)
- **aria-allowed-attr:** flag deprecated ARIA attributes as needs-review
([#5246](#5246))
([518f3cc](518f3cc)),
closes [#3341](#3341)
- **aria-prohibited-attr:** allow many elements to be named and disallow
label and body from being named
([#5259](#5259))
([d8b1ea5](d8b1ea5))
- **aria-roles:** add sectionheader and sectionfooter roles
([#5238](#5238))
([c36c109](c36c109)),
closes [#4734](#4734),
references [#4734](#4734)
- **aria/get-aria-value:** new function to get aria values of a node
([#5109](#5109))
([a7d8f3e](a7d8f3e)),
references [#5042](#5042)
- **aria/has-attr-value:** new function to check if node has aria value
([#5136](#5136))
([61f2624](61f2624)),
references [#5109](#5109)
- **aria:** support role=image as equivalent to role=img
([#5248](#5248))
([5aa8aaf](5aa8aaf)),
closes [#4656](#4656),
references [#5272](#5272)
- **checks/aria:** support ARIA element internals properties
([#5172](#5172))
([9b7f754](9b7f754))
- **checks/label:** support ARIA element internals properties
([#5170](#5170))
([21c5f8b](21c5f8b))
- **checks/navigation:** support ARIA element internals properties
([#5167](#5167))
([2c3a98f](2c3a98f))
- **commons/aria:** support ARIA element internals properties
([#5171](#5171))
([31f09e7](31f09e7))
- **commons/dom:** support ARIA element internals properties
([#5163](#5163))
([f0a12cf](f0a12cf))
- **commons/forms:** support ARIA element internals properties
([#5165](#5165))
([27a4686](27a4686))
- **commons/matches/fromPrimative:** deprecate in favor of correct
spelling ([#5270](#5270))
([31cfb2e](31cfb2e))
- **commons/text:** support ARIA element internals properties
([#5169](#5169))
([e841a33](e841a33))
- **commons/text:** support form-associated labels via element internals
([#5182](#5182))
([57cfe0a](57cfe0a)),
closes [#5045](#5045),
references [#5170](#5170)
[#5039](#5039)
[#5151](#5151)
[#5039](#5039)
- **dom/getResolvedRefs:** new function to get the resolved virtual
nodes of idrefs
([#5151](#5151))
([489cdea](489cdea)),
references [#5109](#5109)
- **element-internals:** enable ElementInternals by default
([#5284](#5284))
([2740d42](2740d42)),
closes [#5277](#5277)
- **i18n:** Add Swedish locale
([#5190](#5190))
([dcd13f2](dcd13f2)),
references [#5189](#5189)
- **matches:** add inSectioningContent, hasChild, and
isSummaryForDetails matches
([#5262](#5262))
([c47cdcd](c47cdcd))
- **rules:** support ARIA element internals properties
([#5168](#5168))
([065baf7](065baf7))
- **standards/ariaAttrs:** add caseInsensitive property for attributes
([#5224](#5224))
([bcd791c](bcd791c))

### Bug Fixes

- **aria-allowed-role:** allow roles on a non-details summary
([#5242](#5242))
([3bd9875](3bd9875)),
closes [#3911](#3911),
references [#3443](#3443)
[#3911](#3911)
- **aria-allowed-role:** restrict figure roles with child figcaption
([#5240](#5240))
([178a635](178a635)),
closes [#3443](#3443)
- **aria-prohibited-attr:** visible aria-labelledby requires review only
([#5285](#5285))
([fd6fa9f](fd6fa9f))
- **axe.d.ts:** make enabled property of RuleMetadata optional
([#5129](#5129))
([90fce18](90fce18))
- **color-contrast:** fix various stacking context bugs
([#5214](#5214))
([d5e5b04](d5e5b04)),
references [#8](#8)
[#5213](#5213)
- **gather-internals:** handle non-HTMLElement nodes
([#5161](#5161))
([06e84c3](06e84c3))
- **get-selector:** escape control characters in attribute selectors
([#5273](#5273))
([4b60ac5](4b60ac5)),
closes [#5204](#5204)
[#5204](#5204)
- **image-alt:** allow whitespace alt on presentational images
([#5218](#5218))
([c5dd0ef](c5dd0ef)),
closes [#5216](#5216)
- **landmark-unique:** exclude section/form with non-landmark roles from
landmark match
([#5085](#5085))
([c5fd013](c5fd013)),
closes [#4722](#4722)
[#5064](#5064)
- name the image role in role-img-alt and svg-img-alt metadata
([#5279](#5279))
([995a269](995a269)),
closes [#5272](#5272),
references [#5248](#5248)
[#5248](#5248)
- **standards:** update aria-errormessage and aria-details to be idrefs
([#5157](#5157))
([fb94f8a](fb94f8a))

This PR was opened by a robot 🤖 🎉