Parses imports
SimpleXMLElement $xml:
string $file:
private function parseImports(SimpleXMLElement $xml, $file) {
  if (false === ($imports = $xml
    ->xpath('//container:imports/container:import'))) {
    return;
  }
  foreach ($imports as $import) {
    $this
      ->setCurrentDir(dirname($file));
    $this
      ->import((string) $import['resource'], null, (bool) $import
      ->getAttributeAsPhp('ignore-errors'), $file);
  }
}