docs: Mention <packing> in migration guide

Add another hint for what to do with child properties.

Fixes: #3950

diff --git a/docs/reference/gtk/migrating-3to4.md b/docs/reference/gtk/migrating-3to4.md
index a97f9ea8bb50e3043a58af50c06aa24cb1e7b4e3..ad0f248c18c56352c7dbc2d6eb1e4cd971cd7dfd 100644 (file)
--- a/docs/reference/gtk/migrating-3to4.md
+++ b/docs/reference/gtk/migrating-3to4.md
@@ -804,6 +804,11 @@ by a layout manager (if they are layout-related), or handled in some
 other way. One possibility is to use child meta objects, as seen with
 [class@Gtk.AssistantPage], [class@Gtk.StackPage] and the like.
 
+If you used to define child properties with `<packing>` in ui files, you have
+to switch to using `<layout>` for the corresponding layout properties.
+`gtk4-builder-tool` can help with this conversion, with the `--3to4` option
+of the `simplify` command.
+
 The replacements for gtk_container_add() are:
 
 | Widget | Replacement |