code: func (runner *runner) checkRule(table Table, chain Chain, args ...string) (bool, error) {
  	if runner.hasCheck {
  		return runner.checkRuleUsingCheck(makeFullArgs(table, chain, args...))
  	} else {
  		return runner.checkRuleWithoutCheck(table, chain, args...)
  	}
  }
docs: // Returns (bool, nil) if it was able to check the existence of the rule, or
  // (<undefined>, error) if the process of checking failed.