WP_Customize_Setting::_multidimensional_preview_filter PHP Method

    public final function _multidimensional_preview_filter($original)
    {
        if (!$this->is_current_blog_previewed()) {
            return $original;
        }
        $id_base = $this->id_data['base'];
        // If no settings have been previewed yet (which should not be the case, since $this is), just pass through the original value.
        if (empty(self::$aggregated_multidimensionals[$this->type][$id_base]['previewed_instances'])) {
            return $original;
        }
        foreach (self::$aggregated_multidimensionals[$this->type][$id_base]['previewed_instances'] as $previewed_setting) {
            // Skip applying previewed value for any settings that have already been applied.
            if (!empty(self::$aggregated_multidimensionals[$this->type][$id_base]['preview_applied_instances'][$previewed_setting->id])) {
                continue;
            }
            // Do the replacements of the posted/default sub value into the root value.
            $value = $previewed_setting->post_value($previewed_setting->default);
            $root = self::$aggregated_multidimensionals[$previewed_setting->type][$id_base]['root_value'];
            $root = $previewed_setting->multidimensional_replace($root, $previewed_setting->id_data['keys'], $value);
            self::$aggregated_multidimensionals[$previewed_setting->type][$id_base]['root_value'] = $root;
            // Mark this setting having been applied so that it will be skipped when the filter is called again.
            self::$aggregated_multidimensionals[$previewed_setting->type][$id_base]['preview_applied_instances'][$previewed_setting->id] = true;
        }
        return self::$aggregated_multidimensionals[$this->type][$id_base]['root_value'];
    }