@Override
 protected void bindSpec(Iterable<VMSpec> specs, XMLBuilder rootBuilder)
     throws ParserConfigurationException, FactoryConfigurationError {
   rootBuilder.a("name", "");
   XMLBuilder specBuilder = buildChildren(rootBuilder);
   for (VMSpec spec : specs) {
     checkSpec(spec);
     XMLBuilder vAppBuilder = buildRootForName(specBuilder, spec.getName());
     addOperatingSystemAndVirtualHardware(spec, vAppBuilder);
   }
 }