code: function() {
      var container = document.createElement('mutation');
      var isAt1 = this.getInput('AT1').type == Blockly.INPUT_VALUE;
      container.setAttribute('at1', isAt1);
      var isAt2 = this.getInput('AT2').type == Blockly.INPUT_VALUE;
      container.setAttribute('at2', isAt2);
      return container;
    }
docs: Create XML to represent whether there are 'AT' inputs.
  @return {!Element} XML storage element.
  @this Blockly.Block