Update a11y.ts

[OliverSpeir]

Allow for aria-label and aria-labelledby in a11y-missing-content rule

Changes

• What does this change?

  • dev overlay axe rule for required content
  • https://www.w3.org/WAI/WCAG21/Techniques/aria/ARIA14
  • https://www.w3.org/TR/2008/REC-WCAG20-20081211/#content-structure-separation-programmatic
  • This also will align with https://github.com/dequelabs/axe-core rules

• Don't forget a changeset! pnpm exec changeset

  • not sure how to handle this, I tried it but didn't seem correct hopefully someone can help

Testing

unfamiliar with testing honestly, sorry in advance

Docs

docs update unnecessary

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[OliverSpeir]

After researching deeper to answer the question about aria-describedby I realized that if a heading or anchor has an img inside it and that img has an alt property then that alt will become the "accessible name".

I also realized that previously it was only going to check if the element that the aria-labelledby property referenced existed, but what it really should be checking if any one of the IDs have valid text

I did test this by editing my node_modules on a local repo fwiw but if someone can verify it all works that would probably be best 😅

more reference: https://www.w3.org/TR/accname/#dfn-accessible-name

[OliverSpeir]

Tried to improve readability, as well as return early as @fflaten suggested.

Also changed the error message.