import { PipelineOperator } from "../../core";
/**
 * 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}.
 *
 * @param collection
 * @param expr
 * @param options
 * @returns
 */
export declare const $unwind: PipelineOperator;