void addFromString(String string, [ num weight ])

Source 

void addFromString(String string, [num weight]) {
  if (weight != null) {
    _blink.BlinkSpeechGrammarList.instance
        .addFromString_Callback_2_(this, string, weight);
    return;
  }
  _blink.BlinkSpeechGrammarList.instance
      .addFromString_Callback_1_(this, string);
  return;
}