/**
 * Keyboard + roving-tabindex helpers for card-style radio groups.
 *
 * CartPaymethods / CartCarriers / DeliveryDate render their options as styled
 * cards, not `<input type="radio">`, so they got no keyboard or screen-reader
 * affordances for free: the options were plain divs with a click handler —
 * unreachable by Tab, invisible to the accessibility tree, and (because
 * choosing a carrier is required to advance checkout) a hard block for
 * keyboard-only and screen-reader users.
 *
 * Rather than restyle three components around native inputs, they keep their
 * markup and adopt the ARIA radiogroup pattern. These two helpers are the
 * whole behavioural contract, shared so the three stay consistent.
 */
/**
 * `keydown` handler for an element carrying `role="radio"`.
 *
 * Enter/Space selects; arrow keys move focus to the previous/next radio in the
 * enclosing `role="radiogroup"` and select it, which is how native radios
 * behave. Selection is driven by dispatching a real `click`, so the component's
 * existing `@click` handler stays the single place selection is implemented —
 * no second code path to keep in sync.
 */
export declare function radioGroupKeydown(event: KeyboardEvent): void;
/**
 * Roving tabindex: exactly ONE radio in a group is tabbable, so Tab enters and
 * leaves the group as a single stop and the arrow keys move within it.
 *
 * The selected option owns the tab stop. With nothing selected yet the first
 * option takes it — otherwise the group would have no tabbable element at all
 * and a keyboard user could never reach it, which is the state checkout starts
 * in.
 */
export declare function radioTabIndex(isSelected: boolean, index: number, hasSelection: boolean): number;