[gtk/wip/matthiasc/can-focus: 31/31] Mention focus changes in the migration guide

[Matthias Clasen <matthiasc src gnome org>]

commit f16c8291907b523ce3a809623b0a67366c3e4039
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Apr 9 17:29:48 2020 -0400

    Mention focus changes in the migration guide

 docs/reference/gtk/migrating-3to4.xml | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
---
diff --git a/docs/reference/gtk/migrating-3to4.xml b/docs/reference/gtk/migrating-3to4.xml
index 634fcbe71d..570bdca0d7 100644
--- a/docs/reference/gtk/migrating-3to4.xml
+++ b/docs/reference/gtk/migrating-3to4.xml
@@ -470,6 +470,22 @@
       </para>
     </section>
 
+    <section>
+      <title>Focus handling changes</title>
+      <para>
+        The semantics of the #GtkWidget:can-focus property have changed.
+        In GTK 3, this property only meant that the widget itself would not
+        accept keyboard input, but its children still might (in the case of
+        containers). In GTK 4, if :can-focus is %FALSE, the focus cannot enter
+        the widget or any of its descendents, and the default value has changed
+        from %FALSE to %TRUE.
+      </para>
+      <para>
+        The recommended way to influence focus behavior of custom widgets
+        in GTK 4 is to override the focus() and grab_focus() vfuncs.
+      </para>
+    </section>
+
     <section>
       <title>Stop using GtkEventBox</title>
       <para>