Specs: Drop @nonnull from dom.md, drop ChildNode from dom.md, drop TreeRoot from dom.md, other mino…

sky/specs/events.md

 Sky Event Model
 ===============
 
 ```dart
 SKY MODULE
 <!-- part of sky:core -->
 
 <script>
 import 'dart:collection';
 import 'dart:async';
@@ skipping 113 matching lines @@
   EventTarget get currentTarget => _currentTarget;
 
   bool handled; // precise semantics depend on the event type, but in general, set this when you set result
   ReturnType result;
 
   bool resultIsCompatible(dynamic candidate) => candidate is ReturnType;
 
   // TODO(ianh): abstract API for doing things at shadow tree boundaries 
   // TODO(ianh): do events get blocked at scope boundaries, e.g. focus events when both sides are in the scope?
   // TODO(ianh): do events get retargetted, e.g. focus when leaving a custom element?
+  // e.g. sent from inside a shadow tree, when exiting the shadow tree, focus event should:
+  //  - disappear if we're moving from one to another element
+  //  - be targetted if it's going to another node in a different scope
 }
 
 class EventTarget {
   EventTarget() : _eventsController = new DispatcherController<Event>();
 
   Dispatcher get events => _eventsController.dispatcher;
   EventTarget parentNode;
 
   List<EventTarget> getEventDispatchChain() {
     if (this.parentNode == null) {
@@ skipping 32 matching lines @@
     return event.result;
   }
 
   void _dispatchEventLocally(Event event) {
     event._currentTarget = this;
     _eventsController.add(event);
   }
 }
 </script>
 ```