[gtk/stackpage: 9/11] migration guide: Mention --3to4

[Matthias Clasen <matthiasc src gnome org>]

commit edd3f28a1d7713d77fa5267c8453b2001b79437f
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Feb 7 13:12:07 2019 -0500

    migration guide: Mention --3to4

 docs/reference/gtk/migrating-3to4.xml | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
---
diff --git a/docs/reference/gtk/migrating-3to4.xml b/docs/reference/gtk/migrating-3to4.xml
index c5e9ef148c..4fbafaa6a8 100644
--- a/docs/reference/gtk/migrating-3to4.xml
+++ b/docs/reference/gtk/migrating-3to4.xml
@@ -329,6 +329,17 @@
       </para>
     </section>
 
+    <section>
+      <title>Adapt to GtkStack API changes</title>
+      <para>
+        The GtkStack child properties have been converted into child meta object.
+        Instead of gtk_container_child_set (stack, child, …), you can now use
+        g_object_set (gtk_stack_get_page (stack, child), …). In .ui files, the
+        GtkStackPage objects must be created explicitly, and take the child widget
+        as property. gtk4-builder-tool can help with this conversion.
+      </para>
+    </section>
+
     <section>
       <title>Adapt to GtkStyleContext API changes</title>
       <para>
@@ -574,6 +585,14 @@
       </para>
     </section>
 
+    <section>
+      <title>Convert .ui files</title>
+      <para>
+        The simplify command of gtk4-builder-tool has gained a --3to4 option, which
+        can help with some of the required changes in .ui files, such as converting
+        child properties to child meta objects.
+      </para>
+    </section>
   </section>
 
 </chapter>