CharArrayWriter caw = new CharArrayWriter();
SerializationContextImpl sci = new SerializationContextImpl(caw);
sci.setDoMultiRefs(true);
sci.serialize(new QName("someLocalPart"), null, tb1);
sci.serialize(new QName("someOtherLocalPart"), null, tb2);
String s = caw.toString();
// Cheap but fragile.
int first = s.indexOf("#id0");