static void attachHead(Document document)
    {
        Head head = new Head(document, document);

        Title title = new Title(head, document);
        title.text = "Hello world from protostuff-runtime graph ser/deser!";

        Link link = new Link(head, document);
        link.rel = "shortcut icon";
        link.href = "/favicon.ico";
        link.type = "image/x-icon";
    }
Test ser/deser of polymorphic graph objects (references and cyclic dependencies).

@author David Yu
@created Jan 19, 2011
protostuff-runtime/src/test/java/io/protostuff/runtime/PolymorphicRuntimeGraphTest.java