code: def __eval_validator_check(self, check_item, resp_obj):
          
          if isinstance(check_item, (dict, list)) \
              or isinstance(check_item, parser.LazyString):
              # format 1/2/3
              check_value = self.eval_content(check_item)
          else:
              # format 4/5
              check_value = resp_obj.extract_field(check_item)
  
          return check_value
docs: evaluate check item in validator.
  
          Args:
              check_item: check_item should only be the following 5 formats:
                  1, variable reference, e.g. $token
                  2, function reference, e.g. ${is_status_code_200($status_code)}
                  3, dict or list, maybe containing variable/function reference, e.g. {"var": "$abc"}
                  4, string joined by delimiter. e.g. "status_code", "headers.content-type"
                  5, regex string, e.g. "LB[\d]*(.*)RB[\d]*"
  
              resp_obj: response object