LiveViewContinuity.Disclosure.disclosure/1 is an unstyled standalone disclosure whose effective expanded state is owned by the browser. Required inputs are a stable id, exactly one rich trigger slot, and exactly one always-mounted panel body. default_expanded defaults to false and only seeds SSR or a newly mounted instance. Root, trigger, and panel classes are consumer-owned; global attributes apply to the root.
The trigger is a native button type="button" with stable aria-controls and browser-reflected aria-expanded. The panel has a stable aria-labelledby backlink and browser-reflected hidden and aria-hidden. Pointer, Enter, and Space use native button activation. Each activation changes the effective state immediately without sending a LiveView event or waiting for server acknowledgment.
LiveView owns the trigger and panel content and may patch either subtree. The browser owns root data-lvc-open, trigger aria-expanded, and panel hidden/aria-hidden; only those attributes are ignored narrowly. A retained-root patch therefore preserves effective expanded state even when the server continues to render the original default_expanded, while panel content remains patchable. A newly mounted root starts from the current server-rendered default.
data-lvc-open="true|false" is the stable styling and test hook. Consumers should derive indicator rotation or other visual changes from it rather than maintaining another state copy.
Disclosure is intentionally distinct from LiveViewContinuity.Accordion: Disclosure is one browser-owned boolean with no event, while Accordion coordinates server-authoritative logical values and acknowledgment. Controlled expanded state, server callbacks, grouped disclosures, required-open behavior, heading wrappers, region landmarks, animations, conditional unmount, hidden="until-found", detached or multiple triggers, and navigation-persistent state remain outside this contract. There is no shared Disclosure/Accordion state-machine abstraction in this slice.