code: public function errorSummary($models, $options = [])
      {
          Html::addCssClass($options, $this->errorSummaryCssClass);
          $options['encode'] = $this->encodeErrorSummary;
          return Html::errorSummary($models, $options);
      }
docs: Generates a summary of the validation errors.
  If there is no validation error, an empty error summary markup will still be generated, but it will be hidden.
  @param Model|Model[] $models the model(s) associated with this form.
  @param array $options the tag options in terms of name-value pairs. The following options are specially handled:
  
  - `header`: string, the header HTML for the error summary. If not set, a default prompt string will be used.
  - `footer`: string, the footer HTML for the error summary.
  
  The rest of the options will be rendered as the attributes of the container tag. The values will
  be HTML-encoded using [[\yii\helpers\Html::encode()]]. If a value is `null`, the corresponding attribute will not be rendered.
  @return string the generated error summary.
  @see errorSummaryCssClass