three.js/src/Three.Legacy.d.ts

import { Geometry } from './core/Geometry';
import { Material } from './materials/Material';
import { Object3D } from './core/Object3D';
import { Scene } from './scenes/Scene';

export namespace SceneUtils {
  export function createMultiMaterialObject(
    geometry: Geometry,
    materials: Material[]
  ): Object3D;
  export function detach(child: Object3D, parent: Object3D, scene: Scene): void;
  export function attach(child: Object3D, scene: Scene, parent: Object3D): void;
}