docstr: Args:
      name (str): the name of the dataset split, e.g. "coco_train2017"
      key: the key of the metadata, e.g., "class_names"
      value: the value of the metadata
code: def register_metadata(name, key, value):
      """
      Args:
          name (str): the name of the dataset split, e.g. "coco_train2017"
          key: the key of the metadata, e.g., "class_names"
          value: the value of the metadata
      """
      DatasetRegistry._metadata_registry[name][key] = value
  
file_path: tensorpack/examples/FasterRCNN/dataset/dataset.py
imports: from collections import defaultdict
label_desc: Use image node_id 3 for calling the DatasetRegistry obj's underlying member method code with example usage: obj.register_metadata(name, key, value) without return types