# TabPanel One `role="tabpanel"` (D67). Every panel renders; unselected ones carry `hidden`. Returning null instead would leave `aria-controls` on every unselected tab pointing at an element that does not exist, and would throw away DOM state — a half-filled form in a panel would lose its values on each tab switch. The cost is a heavier DOM when panels are large; the answer to that is rendering less inside the panel, not unmounting it behind the consumer's back. `tabIndex={0}` because a panel whose content has no focusable element would otherwise be unreachable by keyboard. ## Props | Prop | Type | Default | Required | Description | |---|---|---|---|---| | `value` | `string` | — | yes | Pairs this panel with the `Tab` of the same value. | | `children` | `ReactNode` | — | yes | The view for this tab. Rendered even when unselected, then `hidden`. | | `className` | `string` | — | no | Additional CSS class name(s) merged onto the component's root element. | | `ref` | `Ref` | — | no | Forwarded ref to the panel element. | ## Keyboard & assistive tech | Keys | Behavior | |---|---| | Tab | The panel itself is a tab stop (tabIndex=0), so a panel whose content has no focusable element is still reachable. | Renders role="tabpanel" with aria-labelledby pointing back at its tab. Unselected panels stay in the DOM with `hidden`. ## Theming This component has no `--psi-tab-panel-*` tokens — its styling binds scale tokens only, so there is nothing component-scoped to override. Theme changes reach it through the semantic tokens of its children and surroundings. ## Rules - One accent per visual group; everything else neutral or ghost. - danger only for actions with real consequences. - Sizes are px numbers (24|32|40|48), never S/M/L. - Typography tokens are --psi-text-{size}-{lineHeight}-{weight}. - Override component tokens (--psi-{component}-*), not semantic tokens, for one-off theming. - --psi-button-font overrides button typography across all sizes (documented D34 override; ember → mono). - Wrap labeled form controls in Field — label association, description/error line, aria-describedby and aria-invalid come wired; don't hand-roll label+message rows. - Field is for a control with a *visible* label. A toolbar filter control named by aria-label or placeholder takes neither a Field nor a hand-rolled label row — compare filter-toolbar (no labels) with table-pagination ("Rows per page" visible, so Field). - Use Dialog for blocking modal flows — title/footer slots, dismissible gate; danger stays on the footer Buttons, one accent per group.