Added some more documentation to top level Window.

sdk/lib/html/dart2js/html_dart2js.dart

Index: sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index b218ef9311ab8be8c32783913e9f777491024bcd..ba5eade152615dc25ed3aedd756783fde3f99f79 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -38,12 +38,22 @@ import 'dart:_foreign_helper' show JS;
 
 
 /**
- * The top-level Window object.
+ * Top-level container for a web page, which is usually a browser tab or window.
+ *
+ * Each web page loaded in the browser has its own [Window], which is a
+ * container for the web page.
+ *
+ * This getter usually retuns the only [Window] on the page, but any `<iframe>`

[Kathy Walrath, 2013/07/11 18:31:39]

retuns -> returns

This sentence makes it sound like this getter might sometimes return another
window or multiple windows. Maybe (as a continuation of the paragraph above):

If the web page has `<iframe>`s, then each iframe has its own window object,
which is accessible only to that iframe. 

[Andrei Mouravski, 2013/07/11 20:52:05]

Done.

+ * elements have their own [Window].
+ *
+ * See also:
+ *
+ *   * [Window](https://developer.mozilla.org/en-US/docs/Web/API/window) from MDN.
  */
 Window get window => JS('Window', 'window');
 
 /**
- * The top-level Document object.
+ * Root node for all content in a web page.
  */
 HtmlDocument get document => JS('HtmlDocument', 'document');