code: def key_rule(self, regex, verifier):
          
  
          if regex is not None:
              regex = re.compile(regex)
  
          self._additional_key_rules.append((regex, verifier))
docs: Add a rule with a pattern that should apply to all keys.
  
          Any key not explicitly listed in an add_required or add_optional rule
          must match ONE OF the rules given in a call to key_rule().
          So these rules are all OR'ed together.
  
          In this case you should pass a raw string specifying a regex that is
          used to determine if the rule is used to check a given key.
  
  
          Args:
              regex (str): The regular expression used to match the rule or None
                  if this should apply to all
              verifier (Verifier): The verification rule