class_docstr: Clip bounding box to image edges.
  
  Parameters
  ----------
  axis : int
      The coordinate axis with length 4.
docstr: Backward gradient is passed through.
docstr_tok: ["Backward","gradient","is","passed","through","."]
code: def backward(self, req, out_grad, in_data, out_data, in_grad, aux):
      """Backward gradient is passed through."""
      self.assign(in_grad[0], req[0], out_grad[0])
  
file_path: gluon-cv/gluoncv/model_zoo/rcnn/rpn/bbox_clip.py
imports: import mxnet
label_desc: Use image node_id 3 for calling the BBoxClipToImage obj's underlying member method code with example usage: obj.backward(req, out_grad, in_data, out_data, in_grad, aux) without return types