code: function(xmlElement) {
      var isAt1 = (xmlElement.getAttribute('at1') == 'true');
      var isAt2 = (xmlElement.getAttribute('at2') == 'true');
      this.updateAt_(1, isAt1);
      this.updateAt_(2, isAt2);
    }
docs: Parse XML to restore the 'AT' inputs.
  @param {!Element} xmlElement XML storage element.
  @this Blockly.Block