import { Iterator } from "../../lazy";
import { Options } from "../../types";
/**
 * Deconstructs an array field from the input documents to output a document for each element. Each output document replaces the array with an element value.
 * For each input document, outputs n documents where n is the number of array elements and can be zero for an empty array.
 *
 * See {@link https://www.mongodb.com/docs/manual/reference/operator/aggregation/unwind/ usage}.
 */
export declare function $unwind(coll: Iterator, expr: string | {
    path: string;
    includeArrayIndex?: string;
    preserveNullAndEmptyArrays?: boolean;
}, _options: Options): Iterator;