xstream.alias("container", ExtenalizableContainer.class);
xstream.alias("original-class", Original.class);
xstream.alias("replaced-class", Replaced.class);
ExtenalizableContainer in = new ExtenalizableContainer();
in.original = new Original("hello world");
String xml = ""
+ "<container>\n"
+ " <original-class resolves-to=\"replaced-class\" class=\"not.Existing\">\n"
+ " <replacedValue>HELLO WORLD</replacedValue>\n"