MessageWriter child1 = writer.getElementWriter("child1", "urn:child1");
MessageWriter att1 = child1.getAttributeWriter("att1");
att1.writeValue("att1");
att1.close();
MessageWriter att2 = child1.getAttributeWriter("att2", "");
att2.writeValue("att2");
att2.close();
MessageWriter att3 = child1.getAttributeWriter("att3", "urn:att3");
att3.writeValue("att3");
att3.close();
MessageWriter att4 = child1.getAttributeWriter("att4", null);