function readMetadataURL(node, objectStack) {
  const metadataObject = readFormatOnlineresource(node, objectStack);
  if (metadataObject) {
    metadataObject['type'] = node.getAttribute('type');
    return metadataObject;
  }
  return undefined;
}
@param {Element} node Node.
@param {Array<*>} objectStack Object stack.
@return {Object|undefined} Metadata URL object.