[gtk+] Add more CSS node docs

[Matthias Clasen <matthiasc src gnome org>]

commit 029aad7907a2381e398a601d25907c39cf9b332b
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Nov 19 14:01:41 2015 -0500

    Add more CSS node docs

 gtk/gtkcssnode.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtkcssnode.c b/gtk/gtkcssnode.c
index 6727d9f..560f306 100644
--- a/gtk/gtkcssnode.c
+++ b/gtk/gtkcssnode.c
@@ -61,6 +61,11 @@
  * - The draw function should just use gtk_style_context_save_to_node() to
  *   'switch' to the right node, not make any other changes to the style
  *   context.
+ *
+ * A noteworthy difference between gtk_style_context_save() and
+ * gtk_style_context_save_to_node() is that the former inherits all the
+ * style classes from the main CSS node, which often leads to unintended
+ * inheritance. 
  */
 
 /* When these change we do a full restyling. Otherwise we try to figure out