import * as functions from 'firebase-functions';
/**
 * Update a tag collection automatically
 * @param change - functions
 * @param context - event context
 * @param field - name of tags field in document
 * @param tagCol - name of tag index collection
 * @param createAllTags - boolean - create a doc '_all' containing all tags
 * @param aggregateField - the name of the field to aggregate, default tagAggregate
 * @param allTagsName - name of all tags doc, default '_all'
 * @param maxNumTags - the maximum number of tags to put in a doc, default is 100
 */
export declare function tagIndex(change: functions.Change<functions.firestore.DocumentSnapshot>, context: functions.EventContext, field?: string, tagCol?: string, createAllTags?: boolean, aggregateField?: string, allTagsName?: string, maxNumTags?: number): Promise<null>;