Index: gtk/gtktooltip.c
===================================================================
diff -Nup gtk/.svn/text-base/gtktooltip.c.svn-base gtk/gtktooltip.c
--- gtk/gtktooltip.c	(revision 18662)
+++ gtk/gtktooltip.c	(working copy)
@@ -486,6 +486,9 @@ child_location_foreach (GtkWidget *child
     }
 }
 
+/* translates coordinates from dest_widget->window relative (src_x,src_y)
+ * to allocation relative (dest_x,dest_y) of dest_widget.
+ */
 static void
 window_to_alloc (GtkWidget *dest_widget,
 		 gint       src_x,
@@ -498,7 +501,7 @@ window_to_alloc (GtkWidget *dest_widget,
     {
       gint wx, wy;
       gdk_window_get_position (dest_widget->window, &wx, &wy);
-
+      /* offset coordinates if widget->window is smaller than widget->allocation */
       src_x += wx - dest_widget->allocation.x;
       src_y += wy - dest_widget->allocation.y;
     }
@@ -514,6 +517,9 @@ window_to_alloc (GtkWidget *dest_widget,
     *dest_y = src_y;
 }
 
+/* translates coordinates from window relative (x,y) to
+ * allocation relative (x,y) of the returned widget.
+ */
 static GtkWidget *
 find_widget_under_pointer (GdkWindow *window,
 			   gint      *x,
@@ -581,6 +587,9 @@ find_widget_under_pointer (GdkWindow *wi
   return event_widget;
 }
 
+/* ignores (x,y) on input. translates event coordinates
+ * to allocation relative (x,y) of the returned widget.
+ */
 static GtkWidget *
 find_topmost_widget_coords_from_event (GdkEvent *event,
 				       gint     *x,
