kartik\select2\Select2::embedAddon PHP Method

    protected function embedAddon($input)
    {
        if (empty($this->addon)) {
            return $input;
        }
        $group = ArrayHelper::getValue($this->addon, 'groupOptions', []);
        $size = isset($this->size) ? ' input-group-' . $this->size : '';
        Html::addCssClass($group, 'input-group' . $size);
        $prepend = ArrayHelper::getValue($this->addon, 'prepend', '');
        $append = ArrayHelper::getValue($this->addon, 'append', '');
        if ($this->pluginLoading) {
            Html::addCssClass($group, 'kv-input-group-hide');
            Html::addCssClass($group, 'group-' . $this->options['id']);
        }
        if (is_array($prepend)) {
            $content = ArrayHelper::getValue($prepend, 'content', '');
            if (isset($prepend['asButton']) && $prepend['asButton'] == true) {
                $prepend = Html::tag('div', $content, ['class' => 'input-group-btn']);
            } else {
                $prepend = Html::tag('span', $content, ['class' => 'input-group-addon']);
            }
            Html::addCssClass($group, 'select2-bootstrap-prepend');
        }
        if (is_array($append)) {
            $content = ArrayHelper::getValue($append, 'content', '');
            if (isset($append['asButton']) && $append['asButton'] == true) {
                $append = Html::tag('div', $content, ['class' => 'input-group-btn']);
            } else {
                $append = Html::tag('span', $content, ['class' => 'input-group-addon']);
            }
            Html::addCssClass($group, 'select2-bootstrap-append');
        }
        $addonText = $prepend . $input . $append;
        $contentBefore = ArrayHelper::getValue($this->addon, 'contentBefore', '');
        $contentAfter = ArrayHelper::getValue($this->addon, 'contentAfter', '');
        return Html::tag('div', $contentBefore . $addonText . $contentAfter, $group);
    }