reducer.setUnderlyingReceiver(builder);
Receiver tree = reducer;
tree.setConfiguration(config);
builder.setConfiguration(config);
tree.open();
int resultSequence = pool.allocate("result", RESULT_NS, "sequence");
int resultDocument = pool.allocate("result", RESULT_NS, "document");
int resultElement = pool.allocate("result", RESULT_NS, "element");
int resultAttribute = pool.allocate("result", RESULT_NS, "attribute");