Clarify some details of global objects implementation.

Review URL: http://codereview.chromium.org/6386011

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6525 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

include/v8.h

@@ -3053,7 +3053,22 @@ class V8EXPORT ExtensionConfiguration {
  */
 class V8EXPORT Context {
  public:
-  /** Returns the global object of the context. */
+  /**
+   * Returns the global proxy object or global object itself for
+   * detached contexts.
+   *
+   * Global proxy object is a thin wrapper whose prototype points to
+   * actual context's global object with the properties like Object, etc.
+   * This is done that way for security reasons (for more details see
+   * https://wiki.mozilla.org/Gecko:SplitWindow).
+   *
+   * Please note that changes to global proxy object prototype most probably
+   * would break VM---v8 expects only global object as a prototype of
+   * global proxy object.
+   *
+   * If DetachGlobal() has been invoked, Global() would return actual global
+   * object until global is reattached with ReattachGlobal().
+   */
   Local<Object> Global();
 
   /**