/**
 * Which tab an arrow key moves to.
 *
 * Separated from the DOM handler because the rules are the part with edge
 * cases — wrapping past either end, Home/End, and leaving every other key
 * alone so typing still reaches the page — and because a component that needs
 * a whole document, component metadata and a live iframe to mount is a poor
 * place to check them.
 *
 * The pattern is the one the ARIA authoring practices describe for a tablist:
 * arrows move and select, Home and End jump to the ends, and focus follows
 * selection so the roving tabindex never leaves focus on an unselected tab.
 */
export declare function nextTabIndex(key: string, current: number, count: number): number | null;