class_docstr: RefCOCO dataset.
  
  The `Refcoco` and `Refcoco+` dataset is based on
  `ReferItGame: Referring to Objects in Photographs of Natural Scenes
  <http://tamaraberg.com/papers/referit.pdf>`_.
  
  The `Refcocog` dataset is based on
  `Generation and Comprehension of Unambiguous Object Descriptions
  <https://arxiv.org/abs/1511.02283>`_.
  
  Args:
      ann_file (str): Annotation file path.
      data_root (str): The root directory for ``data_prefix`` and
          ``ann_file``. Defaults to ''.
      data_prefix (str): Prefix for training data.
      split_file (str): Split file path.
      split (str): Split name. Defaults to 'train'.
      text_mode (str): Text mode. Defaults to 'random'.
      **kwargs: Other keyword arguments in :class:`BaseDataset`.
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code: def _join_prefix(self):
      if not mmengine.is_abs(self.split_file) and self.split_file:
          self.split_file = osp.join(self.data_root, self.split_file)
  
      return super()._join_prefix()
  
file_path: mmdetection/mmdet/datasets/refcoco.py
imports: import collections
  import os.path
  import random
  from typing import Dict, List
  import mmengine
  from mmengine.dataset import BaseDataset
  from mmdet.registry import DATASETS
label_desc: Use image node_id 2 for calling the RefCocoDataset obj's underlying member method code with example usage: obj._join_prefix() and returns: super