code: function updateExpression(value) {
  
        // Rather than passing undefined to the jqLite toggle class function we explicitly set the
        // value to true. Otherwise the class will be just toggled instead of being forced.
        if (angular.isUndefined(value)) {
          value = true;
        }
  
        element.toggleClass('md-autofocus', !!value);
      }
docs: Updates the autofocus class which is used to determine whether the attribute
  expression evaluates to true or false.
  @param {string|boolean} value Attribute Value