code: public java.lang.String getRuleId() {
      java.lang.Object ref = ruleId_;
      if (ref instanceof java.lang.String) {
        return (java.lang.String) ref;
      } else {
        com.google.protobuf.ByteString bs = 
            (com.google.protobuf.ByteString) ref;
        java.lang.String s = bs.toStringUtf8();
        if (bs.isValidUtf8()) {
          ruleId_ = s;
        }
        return s;
      }
    }
docs: <pre>
  Gives the rule an unique ID that can be used for extending in other rules
  through 'extends'. An example of ID is 'closure:innerHtml'.
  </pre>
  
  <code>optional string rule_id = 9;</code>