Add overridable tree binding/unbinding behaviour.

src/components/script/dom/element.rs

@@ -727,4 +727,22 @@ impl VirtualMethods for JS<Element> {
 
         self.notify_attribute_changed(name);
     }
+
+    fn bind_to_tree(&mut self) {
+        match self.super_type() {
+            Some(ref mut s) => s.bind_to_tree(),
+            _ => (),
+        }
+
+        self.bind_to_tree_impl();
+    }
+
+    fn unbind_from_tree(&mut self) {
+        match self.super_type() {
+            Some(ref mut s) => s.unbind_from_tree(),
+            _ => (),
+        }
+
+        self.unbind_from_tree_impl();
+    }
 }

src/components/script/dom/node.rs

@@ -19,12 +19,12 @@ use dom::comment::Comment;
 use dom::document::{Document, HTMLDocument, NonHTMLDocument};
 use dom::documentfragment::DocumentFragment;
 use dom::documenttype::DocumentType;
-use dom::element::{Element, ElementTypeId, HTMLAnchorElementTypeId, IElement};
+use dom::element::{Element, ElementTypeId, HTMLAnchorElementTypeId};
 use dom::eventtarget::{EventTarget, NodeTargetTypeId};
 use dom::nodelist::{NodeList};
 use dom::processinginstruction::ProcessingInstruction;
 use dom::text::Text;
-use dom::virtualmethods::VirtualMethods;
+use dom::virtualmethods::{VirtualMethods, vtable_for};
 use dom::window::Window;
 use html::hubbub_html_parser::build_element_from_tag;
 use layout_interface::{LayoutChan, ReapLayoutDataMsg, UntrustedNodeAddress};
@@ -404,10 +404,7 @@ impl NodeHelpers for JS<Node> {
 
         if self.is_in_doc() {
             for node in self.traverse_preorder() {
-                if node.is_element() {
-                    let element: JS<Element> = ElementCast::to(&node).unwrap();
-                    element.bind_to_tree_impl();
-                }
+                vtable_for(&node).bind_to_tree();
             }
         }
 
@@ -420,10 +417,8 @@ impl NodeHelpers for JS<Node> {
         let document = document_from_node(self);
 
         for node in self.traverse_preorder() {
-            if node.is_element() {
-                let element: JS<Element> = ElementCast::to(&node).unwrap();
-                element.unbind_from_tree_impl();
-            }
+            // XXX how about if the node wasn't in the tree in the first place?
+            vtable_for(&node).unbind_from_tree();
         }
 
         document.get().content_changed();

src/components/script/dom/virtualmethods.rs

@@ -42,6 +42,22 @@ pub trait VirtualMethods {
             _ => (),
         }
     }
+
+    /// Called when a Node is appended to a tree that is part of a Document.
+    fn bind_to_tree(&mut self) {
+        match self.super_type() {
+            Some(ref mut s) => s.bind_to_tree(),
+            _ => (),
+        }
+    }
+
+    /// Called when a Node is removed from a tree that is part of a Document.
+    fn unbind_from_tree(&mut self) {
+        match self.super_type() {
+            Some(ref mut s) => s.unbind_from_tree(),
+            _ => (),
+        }
+    }
 }
 
 /// Obtain a VirtualMethods instance for a given Node-derived object. Any