Define collection types as extending a Collection interface

[zspitz]

e.g.

declare namespace Word {
    class GroupShapes {
        private 'Word.GroupShapes_typekey': GroupShapes;
        private constructor();
        readonly Application: Application;
        readonly Count: number;
        readonly Creator: number;
        Item(Index: any): Shape;
        readonly Parent: any;
        Range(Index: any): ShapeRange;
    }
}

could be defined as:

declare class CollectionBase<TItem, TKey = number> {
    readonly Count: number;
    Item(Index: TKey): TItem;
}

declare namespace Word {
    class Shape {
        private 'Word.Shape_typekey': Shape;
        private constructor();
    }

    class GroupShapes extends CollectionBase<Shape, any> {
        private 'Word.GroupShapes_typekey': GroupShapes;
        private constructor();
        readonly Creator: number;
        readonly Parent: any;
    }
}

Playground

Check first that the class has all the members of the Collection class.