export type IntersectCallback = () => void;
export interface IntersectOptions {
    /** Called every time the element enters the viewport. */
    onVisible?: IntersectCallback;
    /** Called every time the element leaves the viewport. */
    onHidden?: IntersectCallback;
    /**
     * Margin around the viewport in CSS syntax (e.g. `"200px"` or `"10%"`).
     * Positive values trigger callbacks before the element fully crosses the
     * viewport edge. Default: `"0px"`.
     */
    rootMargin?: string;
    /**
     * Intersection ratio threshold (0–1) at which callbacks fire.
     * Default: `0`.
     */
    threshold?: number;
}
/**
 * Attach an `IntersectionObserver` to an element and respond to both
 * enter and exit viewport transitions.
 *
 * ```ts
 * html`<div ${onIntersect({
 *   onVisible() { player.play(); },
 *   onHidden()  { player.pause(); },
 * })}></div>`
 *
 * // With options
 * html`<div ${onIntersect({
 *   onVisible() { prefetch(); },
 *   rootMargin: "200px",
 * })}></div>`
 * ```
 */
export declare function onIntersect(options: IntersectOptions): import("lit-html/directive").DirectiveResult<import("lit-html/directive").DirectiveClass>;
/**
 * Fire `callback` every time the element enters the viewport.
 *
 * ```ts
 * // Infinite scroll sentinel
 * html`<div ${onVisible(() => loadNextPage())}></div>`
 *
 * // Prefetch before fully visible
 * html`<div ${onVisible(() => prefetch(), { rootMargin: "300px" })}></div>`
 * ```
 *
 * @param callback  - Called on every enter transition.
 * @param options   - Optional `rootMargin` / `threshold` tuning.
 */
export declare function onVisible(callback: IntersectCallback, options?: Pick<IntersectOptions, "rootMargin" | "threshold">): import("lit-html/directive").DirectiveResult<import("lit-html/directive").DirectiveClass>;
/**
 * Fire `callback` every time the element leaves the viewport.
 *
 * ```ts
 * // Pause when out of view
 * html`<video ${onHidden(() => video.pause())}></video>`
 *
 * // Track when an ad leaves the screen
 * html`<div ${onHidden(() => trackExit())}></div>`
 * ```
 *
 * @param callback  - Called on every exit transition.
 * @param options   - Optional `rootMargin` / `threshold` tuning.
 */
export declare function onHidden(callback: IntersectCallback, options?: Pick<IntersectOptions, "rootMargin" | "threshold">): import("lit-html/directive").DirectiveResult<import("lit-html/directive").DirectiveClass>;
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