framework/widgets/ActiveForm.php
public function registerClientScript()
    {
        $id = $this->options['id'];
        $options = Json::htmlEncode($this->getClientOptions());
        $attributes = Json::htmlEncode($this->attributes);
        $view = $this->getView();
        ActiveFormAsset::register($view);
        $view->registerJs("jQuery('#$id').yiiActiveForm($attributes, $options);");
    }
public function registerClientScript()
    {
        $id = $this->options['id'];
        $options = Json::htmlEncode($this->getClientOptions());
        $attributes = Json::htmlEncode($this->attributes);
        $view = $this->getView();
        ActiveFormAsset::register($view);
        $view->registerJs("jQuery('#$id').yiiActiveForm($attributes, $options);");
    }
This registers the necessary JavaScript code.
@since 2.0.12