class_docstr: - Use ROUGE-2 as [PaLM 2](https://ai.google/static/documents/palm2techreport.pdf)
  - Use Mecab tokenizer for Japanese eval
code: def _rouge(self, item):
      predictions, references = zip(*item)
      res = rouge2_mecab(
          refs=references, preds=predictions, tokenizer=self.tokenizer
      )
      return res["rouge2"]
  
imports: import os
  import inspect
  from lm_eval.utils import rouge2_mecab
  from lm_eval.base import rf, Task
label_desc: Use image node_id 16 for calling the XLSumJa obj's underlying member method code with example usage: obj._rouge(item) and returns: res