code: public SequenceGenerator<Id<T>> getOrCreateSequenceGenerator()
     {
        Node node = childNode.getOrCreate("sequence-generator");
        SequenceGenerator<Id<T>> sequenceGenerator = new SequenceGeneratorImpl<Id<T>>(this, "sequence-generator", childNode, node);
        return sequenceGenerator;
     }
docs: If not already created, a new <code>sequence-generator</code> element with the given value will be created.
  Otherwise, the existing <code>sequence-generator</code> element will be returned.
  @return  a new or existing instance of <code>SequenceGenerator<Id<T>></code>