Switch

Base Switch is an on/off value control. Root owns the persistent checked value and activation route; Thumb is an optional same-domain indicator and never becomes a second input target.

The cataloged family contains:

• base-switch-root (1..1): semantic owner, value owner, focus and activation target;
• base-switch-thumb (0..*): presentational indicator that consumes Root context.

Root and Thumb are exported from @proto.ui/prototypes-base/switch together with asSwitchRoot() and asSwitchThumb(). Root accepts checked, defaultChecked, and disabled, exposes checked and interaction facts, offers focusSelf(), and emits checkedChange.

Controlled mode keeps the owner-provided checked fact until updated input arrives. Uncontrolled activation commits the next checked value locally. Mixed/indeterminate state is not part of Switch; use a Checkbox boundary when that state is required.

Root projects the switch role and checked state on the single focusable control. Thumb is presentational: it has no activation, value ownership, focus target, or independent accessibility control semantics. Base does not prescribe track geometry, motion, color, or variants.

The stable 0.2.0 package exports the Switch family, and the CLI registry exposes the Root and Thumb through base-switch. T-BASE-SWITCH-0001 maps Root criteria to packages/prototypes/base/test/switch.test.ts; current Web adapter projection can be compared directly in this preview.

P-BASE-SWITCH and P-BASE-SWITCH-THUMB are draft. Their presence in a stable package is release evidence, not lifecycle promotion.

• P-BASE-SWITCH
• P-BASE-SWITCH-THUMB
• Switch source
• Switch evidence
• Styled projections: Shadcn Switch and Brutalist Switch