[gtk/ebassi/docs-for-master: 2/3] docs: Mention GdkSurface:mapped

[Emmanuele Bassi <ebassi src gnome org>]

commit 17373c3e778d8a39d68af3decef593b245fa808a
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Wed Jun 9 18:08:31 2021 +0100

    docs: Mention GdkSurface:mapped
    
    It replaces the ::map-event and ::unmap-event signals on GtkWidget.

 docs/reference/gtk/migrating-3to4.md | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/docs/reference/gtk/migrating-3to4.md b/docs/reference/gtk/migrating-3to4.md
index 49f3d6c8dd..f286fc72dc 100644
--- a/docs/reference/gtk/migrating-3to4.md
+++ b/docs/reference/gtk/migrating-3to4.md
@@ -197,6 +197,9 @@ on a one-by-one basis:
  - If you were using `::delete-event` to present a confirmation when using
    the close button of a window, you should use the
    [signal@Gtk.Window::close-request] signal.
+ - If you were using `::map-event` and `::unmap-event` to track a window
+   being mapped, you should use property notification for the
+   [property@Gdk.Surface:mapped] property instead.
 
 ### Set a proper application ID