Method mergeNodes

/**
 * Merges new elements into a source `<fields>` element.
 *
 * @param   \SimpleXMLElement  $source  The source element.
 * @param   \SimpleXMLElement  $new     The new element to merge.
 *
 * @return  void
 *
 * @since   1.7.0
 */
protected static function mergeNodes(\SimpleXMLElement $source, \SimpleXMLElement $new)
{
    // The assumption is that the inputs are at the same relative level.
    // So we just have to scan the children and deal with them.
    // Update the attributes of the child node.
    foreach ($new->attributes() as $name => $value) {
        if (isset($source[$name])) {
            $source[$name] = (string) $value;
        } else {
            $source->addAttribute($name, $value);
        }
    }
    foreach ($new->children() as $child) {
        $type = $child->getName();
        $name = $child['name'];
        // Does this node exist?
        $fields = $source->xpath($type . '[@name="' . $name . '"]');
        if (empty($fields)) {
            // This node does not exist, so add it.
            self::addNode($source, $child);
        } else {
            // This node does exist.
            switch ($type) {
                case 'field':
                    self::mergeNode($fields[0], $child);
                    break;
                default:
                    self::mergeNodes($fields[0], $child);
                    break;
            }
        }
    }
}