docs: def layered(self, images, only_pushable=False):
          """Yield layers of images"""
          if only_pushable:
              operate_on = dict((image, instance) for image, instance in images.items() if instance.image_index)
          else:
              operate_on = images
  
          layers = Layers(operate_on, all_images=images)
          layers.add_all_to_layers()
          for layer in layers.layered:
              buf = []
              for image_name, image in layer:
                  if image.image_index:
                      buf.append((image_name, image))
              if buf:
                  yield buf