function sortTileImageryByLayerIndex(a, b) {
  let aImagery = a.loadingImagery;
  if (!defined(aImagery)) {
    aImagery = a.readyImagery;
  }

  let bImagery = b.loadingImagery;
  if (!defined(bImagery)) {
    bImagery = b.readyImagery;
  }

  return aImagery.imageryLayer._layerIndex - bImagery.imageryLayer._layerIndex;
}
The {@link ClippingPolygonCollection} used to selectively disable rendering inside or outside a list of polygons.

@type {ClippingPolygonCollection}

@private