set orthogonalEndSash(sash) {
        for (const sashItem of this.sashItems) {
            sashItem.sash.orthogonalEndSash = sash;
        }
        this._orthogonalEndSash = sash;
    }
A reference to a sash, perpendicular to all sashes in this {@link SplitView},
located at the right- or bottom-most side of the SplitView.
Corner sashes will be created automatically at the intersections.