yii\web\XmlResponseFormatter::buildXml PHP Method

    protected function buildXml($element, $data)
    {
        if (is_array($data) || $data instanceof \Traversable && $this->useTraversableAsArray && !$data instanceof Arrayable) {
            foreach ($data as $name => $value) {
                if (is_int($name) && is_object($value)) {
                    $this->buildXml($element, $value);
                } elseif (is_array($value) || is_object($value)) {
                    $child = new DOMElement(is_int($name) ? $this->itemTag : $name);
                    $element->appendChild($child);
                    $this->buildXml($child, $value);
                } else {
                    $child = new DOMElement(is_int($name) ? $this->itemTag : $name);
                    $element->appendChild($child);
                    $child->appendChild(new DOMText($this->formatScalarValue($value)));
                }
            }
        } elseif (is_object($data)) {
            $child = new DOMElement(StringHelper::basename(get_class($data)));
            $element->appendChild($child);
            if ($data instanceof Arrayable) {
                $this->buildXml($child, $data->toArray());
            } else {
                $array = [];
                foreach ($data as $name => $value) {
                    $array[$name] = $value;
                }
                $this->buildXml($child, $array);
            }
        } else {
            $element->appendChild(new DOMText($this->formatScalarValue($data)));
        }
    }