code: public function hiddenInput($options = [])
      {
          $options = array_merge($this->inputOptions, $options);
          $this->adjustLabelFor($options);
          $this->parts['{input}'] = Html::activeHiddenInput($this->model, $this->attribute, $options);
  
          return $this;
      }
docs: Renders a hidden input.
  
  Note that this method is provided for completeness. In most cases because you do not need
  to validate a hidden input, you should not need to use this method. Instead, you should
  use [[\yii\helpers\Html::activeHiddenInput()]].
  
  This method will generate the `name` and `value` tag attributes automatically for the model attribute
  unless they are explicitly specified in `$options`.
  @param array $options the tag options in terms of name-value pairs. These will be rendered as
  the attributes of the resulting tag. The values will be HTML-encoded using [[Html::encode()]].
  
  If you set a custom `id` for the input element, you may need to adjust the [[$selectors]] accordingly.
  
  @return $this the field object itself.