[gtk+] notebook: Document the .dnd style class

[Matthias Clasen <matthiasc src gnome org>]

commit 93aac8a86c27a73734af49255a22ba97c9b237f5
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Jan 13 00:24:40 2016 -0500

    notebook: Document the .dnd style class
    
    We should aim to document all style classes that themes
    can encounter during the normal operation of a widget.

 gtk/gtknotebook.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtknotebook.c b/gtk/gtknotebook.c
index f0eef00..68b8230 100644
--- a/gtk/gtknotebook.c
+++ b/gtk/gtknotebook.c
@@ -135,6 +135,8 @@
  * The header node gets one of the style class .top, .bottom,
  * .left or .right, depending on where the tabs are placed. For
  * reorderable pages, the tab node gets the .reorderable-page class.
+ *
+ * A tab node gets the .dnd style class while it is moved with drag-and-drop.
  */