class_docstr: A constraint on chrF (n-gram F-score) difference.
  
  Args:
      max_chrf (int): Max n-gram F-score allowed.
      compare_against_original (bool): If `True`, compare new `x_adv` against the original `x`.
          Otherwise, compare it against the previous `x_adv`.
class_docstr_tok: ["A","constraint","on","chrF","(","n-gram","F-score",")","difference",".","Args",":","max_chrf","(","int",")",":","Max","n-gram","F-score","allowed",".","compare_against_original","(","bool",")",":","If","`","True","`",",","compare","new","`","x_adv","`","against","the","original","`","x","`",".","Otherwise",",","compare","it","against","the","previous","`","x_adv","`","."]
code: def extra_repr_keys(self):
      return ["max_chrf"] + super().extra_repr_keys()
  
imports: import nltk.translate.chrf_score
  from textattack.constraints import Constraint
label_desc: Use image node_id 3 for calling the chrF obj's underlying member method code with example usage: obj.extra_repr_keys() and returns: unknown