Element newRoot = new Element("newRoot");
doc.setRootElement(newRoot);
assertEquals(newRoot, doc.getRootElement());
assertEquals(1, doc.getChildCount());
doc.appendChild(new Comment("test"));
assertEquals(2, doc.getChildCount());
doc.insertChild(new Comment("prolog comment"), 0);
assertEquals(3, doc.getChildCount());
assertTrue(doc.getChild(0) instanceof Comment);
assertTrue(doc.getChild(1) instanceof Element);
assertTrue(doc.getChild(2) instanceof Comment);