@Override
 public Collection<QName> getExpectedChildElements() {
   return Arrays.asList(keyTag.toQName(), valueTag.toQName());
 }
 @Override
 public Accessor getElementPropertyAccessor(String nsUri, String localName) {
   if (tagName.equals(nsUri, localName)) return acc;
   return null;
 }
 @Override
 public Collection<QName> getExpectedChildElements() {
   return Collections.singleton(entryTag.toQName());
 }