declare namespace Ext {
    export namespace util {
        export interface GroupCollectionConfig {
            decoder?: CallableFunction;
            defaultSortDirection?: string;
            extraKeys?: object;
            filters?: Ext.util.FilterCollection | [];
            grouper?: object;
            groups?: Ext.util.GroupCollection;
            keyFn?: CallableFunction;
            listeners?: object;
            multiSortLimit?: number;
            rootProperty?: string;
            sorters?: Ext.util.SorterCollection | [];
            source?: Ext.util.Collection;
        }

        export class GroupCollection extends Ext.util.Collection  {
        }
    }
}