Specs: Make appendChild, prependChild, and setChild return the child; make Dispatcher's unlisten() …

sky/specs/elements.md

Index: sky/specs/elements.md
diff --git a/sky/specs/elements.md b/sky/specs/elements.md
index b3da48b0698271de58f9ff4895fdaa5a3612b12a..37bb95c4c250106f0724864ca35a517e1ee541fa 100644
--- a/sky/specs/elements.md
+++ b/sky/specs/elements.md
@@ -139,10 +139,11 @@ abstract class ParentNode extends Node {
 
   external void _appendChild(Node node); // O(N) in number of descendants
   // node must be Text or Element
-  void appendChild(Node node) {
+  Node appendChild(Node node) {
     if (node is String)
       node = new Text(node);
-    _appendChild(node);    
+    _appendChild(node);
+    return node;
   }
   void append(List nodes) {
     nodes.forEach(appendChild);
@@ -150,10 +151,11 @@ abstract class ParentNode extends Node {
 
   external void _prependChild(Node node); // O(N) in number of descendants
   // node must be Text or Element
-  void prependChild(Node node) {
+  Node prependChild(Node node) {
     if (node is String)
       node = new Text(node);
-    _prependChild(node);    
+    _prependChild(node);
+    return node;
   }
   void prepend(List nodes) {
     // note: not implemented in terms of _prependChild()
@@ -164,9 +166,10 @@ abstract class ParentNode extends Node {
   }
 
   external void removeChildren(); // O(N) in number of descendants
-  void setChild(Node node) {
+  Node setChild(Node node) {
     removeChildren();
     appendChild(node);
+    return node;
   }
   void setChildren(List nodes) {
     removeChildren();