Radio Group

base-radio-group is a draft Base protocol for choosing one value from a visible set. The Root is the sole selected-value owner; Items derive checked and effective disabled state from it, and Indicators only render those facts.

• radio-group-root: owns controlled or uncontrolled value, Collection order, roving focus, group disabled state, and the radiogroup accessibility object
• radio-group-item: contributes one value, projects one focusable radio, and requests selection without owning checked state
• radio-group-indicator: derives checked and disabled facts from its nearest Item; it has no focus, activation, event, or control semantics

The anatomy is deliberately small. The radiogroup is already both the semantic group and the focus collection, so an extra List part would not carry an independent protocol.

Use defaultValue for an uncontrolled initial selection or value for a controlled group. Accepted uncontrolled requests update Root state and emit valueChange once. Controlled requests emit the proposed value but do not create temporary checked state; the next value prop remains authoritative.

Empty and unmatched values are preserved. They produce no checked Item rather than silently selecting the first option. Removing, disabling, or changing the selected Item also leaves the Root value intact; adding a matching Item later restores its derived checked state.

Item values should be non-empty and unique. If duplicate values are authored, only the first matching Item can be checked and a request for that ambiguous value is rejected.

Exactly one enabled Item participates in normal Tab order: the checked enabled Item, otherwise the first enabled Item. Plain focus entry does not invent a selection.

Once focus or keyboard navigation establishes the current Item, unrelated Root updates preserve that tab stop. A controlled value update changes checked state without stealing current focus.

• Space selects the focused enabled Item and prevents page scrolling.
• Right / Down focus and select the next enabled Item.
• Left / Up focus and select the previous enabled Item.
• Home / End focus and select the first or last enabled Item.
• Arrow movement wraps and skips disabled Items.
• Enter does not select outside a future Toolbar-specific protocol.
• focusSelf() moves focus programmatically without changing selection.

Pointer activation focuses and selects only after a successful commit. Canceled input does not select.

Root projects role="radiogroup", dynamic disabled state, and a11yLabel as its explicit accessible name. App Makers must provide a meaningful group name through a11yLabel or an equivalent host projection.

Each Item projects role="radio", boolean aria-checked, effective aria-disabled, and a content-derived name. Indicator is visual feedback only and must not create a second radio object.

This first slice intentionally does not include:

• name, form owner, submission, reset, validation, required, or hidden/native inputs
• native <input type="radio"> event and grouping parity
• public orientation or loop configuration
• Toolbar-specific arrow behavior
• Label or Description parts
• Shadcn/Radix compatibility claims

Those concerns require separate host or semantic contracts; they are not approximated here.

• Catalog: P-BASE-RADIO-GROUP
• Source: packages/prototypes/base/src/radio-group
• Tests: radio-group.test.ts