fix(core): add scope="col" to Table column headers

[bhamodi]

Summary

BaseTable renders every column header as a bare <th> with no scope. In packages/core/src/Table/BaseTable.tsx the per-column initialHeaderHtmlProps (around line 375) set only data-column-key (plus an optional textAlign style) — scope was never emitted, even though TableHeaderCell (packages/core/src/Table/TableHeaderCell.tsx:40) already declares scope?: 'col' | 'row' | 'colgroup' | 'rowgroup' and forwards it to the <th>.

Without scope="col", assistive technology has to guess how header cells relate to data cells. Explicit scope is the reliable, spec-blessed association: it satisfies WCAG 2.1 SC 1.3.1 Info and Relationships (Level A) via technique H63 (using the scope attribute to associate header and data cells), and matches the ARIA APG data-grid expectation that column headers carry the columnheader semantics.

The fix defaults scope: 'col' in initialHeaderHtmlProps, so every column header renders <th scope="col">.

Merge order / override

initialHeaderHtmlProps is the initial value fed into the transformHeaderCell plugin pipeline, which runs before the props are merged onto the <th>. A plugin that writes htmlProps.scope spreads over the default ({...props.htmlProps, scope: ...}), and that value is preserved through the final mergedHtmlProps spread and forwarded by TableHeaderCell. So a consumer-provided scope still wins. The new override test locks this in.

Changes

• packages/core/src/Table/BaseTable.tsx: default scope: 'col' in initialHeaderHtmlProps.
• packages/core/src/Table/Table.test.tsx: added two tests under BaseTable — one asserting every columnheader has scope="col", one asserting a plugin's transformHeaderCell scope override wins (queried via thead th since <th scope="row"> resolves to the rowheader role, not columnheader).

Test plan

• node_modules/.bin/vitest run --root . packages/core/src/Table — 338 pass (16 files), including the 2 new tests (was 336).
• Confirmed failing-first: ran the two new tests before the fix — both failed (getAttribute("scope") === null on the default headers), proving they catch the gap. The override test's first assertion (plugin-set scope="row") passed pre-fix, confirming the plugin scope already flows through the merge.
• tsc --project packages/core/tsconfig.json --noEmit — clean.
• eslint packages/core/src/Table/BaseTable.tsx packages/core/src/Table/Table.test.tsx — clean.

Notes

Found during a broader a11y audit of the Table component. Scoped to this one fix — separate findings (e.g. caption/label props, row-expansion semantics) are intentionally left out. Table.doc.mjs doesn't document header scope semantics, so no doc change was needed.

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[cixzhang]

Thanks @bhamodi — scope="col" on the real column-header s, plugin overrides preserved. 🙏