docs: def cat_boxlist(bboxes):
      """
      Concatenates a list of BoxList (having the same image size) into a
      single BoxList
  
      Arguments:
          bboxes (list[BoxList])
      """
      assert isinstance(bboxes, (list, tuple))
      assert all(isinstance(bbox, BoxList) for bbox in bboxes)
  
      size = bboxes[0].size
      assert all(bbox.size == size for bbox in bboxes)
  
      mode = bboxes[0].mode
      assert all(bbox.mode == mode for bbox in bboxes)
  
      fields = set(bboxes[0].fields())
      assert all(set(bbox.fields()) == fields for bbox in bboxes)
  
      cat_boxes = BoxList(_cat([bbox.bbox for bbox in bboxes], dim=0), size, mode)
  
      for field in fields:
          data = _cat([bbox.get_field(field) for bbox in bboxes], dim=0)
          cat_boxes.add_field(field, data)
  
      return cat_boxes