attach( child, scene, parent ) {

 Matrix4 matrixWorldInverse = parent.matrixWorld.clone();
 matrixWorldInverse.invert();
 child.applyMatrix( matrixWorldInverse );

 scene.remove( child );
 parent.add( child );
}

detach( child, parent, scene ) {
 child.applyMatrix( parent.matrixWorld );
 parent.remove( child );
 scene.add( child );
}

cloneObject(Object3D source) {

 Object3D object;

 // subclass specific properties
 // (must process in order from more specific subclasses to more abstract classes)

 if ( source is MorphAnimMesh ) {

   object = new MorphAnimMesh( source.geometry, source.material );

   (object as MorphAnimMesh).duration = source.duration;
   (object as MorphAnimMesh).mirroredLoop = source.mirroredLoop;
   (object as MorphAnimMesh).time = source.time;

   (object as MorphAnimMesh).lastKeyframe = source.lastKeyframe;
   (object as MorphAnimMesh).currentKeyframe = source.currentKeyframe;

   (object as MorphAnimMesh).direction = source.direction;
   (object as MorphAnimMesh).directionBackwards = source.directionBackwards;

 } else if ( source is SkinnedMesh ) {

   object = new SkinnedMesh( source.geometry, source.material );

 } else if ( source is Mesh ) {

   object = new Mesh( source.geometry, source.material );

 } else if ( source is Line ) {

   object = new Line( source.geometry, source.material, source.type );

 } else if ( source is Ribbon ) {

   object = new Ribbon( source.geometry, source.material );

 } else if ( source is ParticleSystem ) {

   object = new ParticleSystem( source.geometry, source.material );
   (object as ParticleSystem).sortParticles = source.sortParticles;

 } else if ( source is Particle ) {

   object = new Particle( source.material );

 } else if ( source is Sprite ) {

   object = new Sprite();

   (object as Sprite).color.copy( source.color );
   (object as Sprite).map = source.map;
   (object as Sprite).blending = source.blending;

   (object as Sprite).useScreenCoordinates = source.useScreenCoordinates;
   (object as Sprite).mergeWith3D = source.mergeWith3D;
   (object as Sprite).affectedByDistance = source.affectedByDistance;
   (object as Sprite).scaleByViewport = source.scaleByViewport;
   (object as Sprite).alignment = source.alignment;

   (object as Sprite).rotation3d.setFrom(source.rotation3d);
   object.rotation = source.rotation;
   (object as Sprite).opacity = source.opacity;

   (object as Sprite).uvOffset.setFrom(source.uvOffset);
   (object as Sprite).uvScale.setFrom(source.uvScale);

 } else if ( source is LOD ) {

   object = new LOD();

 /*
 } else if ( source instanceof THREE.MarchingCubes ) {

   object = new THREE.MarchingCubes( source.resolution, source.material );
   object.field.set( source.field );
   object.isolation = source.isolation;
 */

 } else if ( source is Object3D ) {

   object = new Object3D();

 }

 // base class properties

 object.name = source.name;

 object.parent = source.parent;

 object.up.setFrom(source.up);

 object.position.setFrom(source.position);

 // because of Sprite madness

 if ( object.rotation is Vector3 ) {
   object.rotation.setFrom(source.rotation);
 }

 object.eulerOrder = source.eulerOrder;

 object.scale.setFrom(source.scale);

 object.isDynamic = source.isDynamic;

 object.renderDepth = source.renderDepth;

 object.rotationAutoUpdate = source.rotationAutoUpdate;

 object.matrix = source.matrix.clone();
 object.matrixWorld = source.matrixWorld.clone();
 object.matrixRotationWorld = source.matrixRotationWorld.clone();

 object.matrixAutoUpdate = source.matrixAutoUpdate;
 object.matrixWorldNeedsUpdate = source.matrixWorldNeedsUpdate;

 object.quaternion.copy( source.quaternion );
 object.useQuaternion = source.useQuaternion;

 object.boundRadius = source.boundRadius;
 object.boundRadiusScale = source.boundRadiusScale;

 object.visible = source.visible;

 object.castShadow = source.castShadow;
 object.receiveShadow = source.receiveShadow;

 object.frustumCulled = source.frustumCulled;

 // children

 for ( var i = 0; i < source.children.length; i ++ ) {

   var child = cloneObject( source.children[ i ] );
   object.children[ i ] = child;

   child.parent = object;

 }

 // LODs need to be patched separately to use cloned children

 if ( source is LOD ) {

   for ( var i = 0; i < source.LODs.length; i ++ ) {

     var slod = source.LODs[ i ];
     var tlod = object as LOD;
     tlod.LODs[ i ] = { "visibleAtDistance": slod.visibleAtDistance, "object3D": tlod.children[ i ] };

   }

 }

 return object;

}

Object3D createMultiMaterialObject( Geometry geometry, materials ) {
 var group = new Object3D();

 materials.forEach((material) {
   group.add(new Mesh(geometry, material));
 });

 return group;

}

void traverseHierarchy( root, callback(node) ) {
 root.children.forEach((n) {
   callback(n);
   traverseHierarchy( n, callback );
 });
}

showHierarchy( root, visible ) => traverseHierarchy( root, (node) => node.visible = visible);