Steps to reproduce

Steps to reproduce

1. Use MUI TreeView with nodes that have partially selected children (indeterminate state) https://stackblitz.com/run?file=src%2FDemo.tsx.
2. Inspect the native <input type="checkbox"> element in the indeterminate state.
3. Notice it uses a data-indeterminate attribute but does not set aria-checked="mixed".
4. Use a screen reader to verify that the indeterminate state is not announced.

Current behavior

• Instead of setting the ARIA state aria-checked="mixed", it uses a custom data-indeterminate attribute.
• Screen readers ignore data-indeterminate, so they do not announce the indeterminate state.

Expected behavior

• The checkbox input should have aria-checked="mixed" when in the indeterminate state.
• This ensures that assistive technologies announce the partial selection properly.

Context

• This behavior breaks WCAG 2.1 Success Criterion 4.1.2 and WAI-ARIA checkbox guidelines. https://www.w3.org/WAI/ARIA/apg/patterns/checkbox/
• Fixing this will improve the experience for screen reader users interacting with TreeView checkboxes.

Your environment

  Don't forget to mention which browser you used.
  Output from `npx @mui/envinfo` goes here.

Search keywords: TreeView, accessibility, aria-check