import { Iterator } from '../../lazy';
import { Options } from '../../core';
/**
 * Processes multiple aggregation pipelines within a single stage on the same set of input documents.
 * Enables the creation of multi-faceted aggregations capable of characterizing data across multiple dimensions, or facets, in a single stage.
 */
export declare function $facet(collection: Iterator, expr: any, options: Options): Iterator;