[gtkmm] Gtk::Builder docs: Describe how to use together with Glib::Property

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 64bc0294e2aa85eb8eb8a25da8320f3c5b0ec802
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Thu Jun 27 18:30:35 2019 +0200

    Gtk::Builder docs: Describe how to use together with Glib::Property

 gtk/src/builder.hg | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)
---
diff --git a/gtk/src/builder.hg b/gtk/src/builder.hg
index 2766ebc4..8fd75783 100644
--- a/gtk/src/builder.hg
+++ b/gtk/src/builder.hg
@@ -37,10 +37,10 @@ _WRAP_GERROR(BuilderError,GtkBuilderError,GTK_BUILDER_ERROR)
  *
  * This object represents an `instantiation' of an UI definition description.
  * When one of these objects is created, the XML file is read, and the user interface
- * is created. The Gtk::Builder object then provides an interface for accessing the
+ * is created. The %Gtk::Builder object then provides an interface for accessing the
  * widgets in the user interface by the names assigned to them inside the UI description.
  *
- * A Gtk::Builder holds a reference to all objects that it has constructed
+ * A %Gtk::Builder holds a reference to all objects that it has constructed
  * and drops these references when it is deleted. This deletion can
  * cause the destruction of non-widget objects or widgets which are not
  * contained in a toplevel window. For toplevel windows constructed by a
@@ -61,6 +61,16 @@ _WRAP_GERROR(BuilderError,GtkBuilderError,GTK_BUILDER_ERROR)
  * Non-widget objects need to be fetched with get_object() or get_objects()
  * to keep them beyond the lifespan of the builder.
  *
+ * @par %Gtk::Builder and Glib::Property
+ * A derived widget that contains Glib::Property members must be registered with
+ * its own name in the GType system. It must be registered before any of the
+ * create_from_*() or add_from_*() methods are called, meaning that you may have
+ * to create an instance of your derived widget just to have its class registered.
+ * There is no reasonably easy way to combine %Gtk::Builder with non-widget objects
+ * containing Glib::Property members. Combining it with widgets containing
+ * Glib::Property members requires glibmm 2.62 or newer.
+ * See also get_widget_derived() and Glib::Property.
+ *
  * @newin{2,12}
  */
 class Builder : public Glib::Object
@@ -544,6 +554,16 @@ public:
    * The following calls will return a pointer to the widget instance that
    * was constructed by the first call.
    *
+   * @par %Gtk::Builder and Glib::Property
+   * If the widget contains Glib::Property members, your constructor must call
+   * the Glib::ObjectBase constructor with a new GType name:
+   * @code
+   * MyDerivedDialog::MyDerivedDialog(BaseObjectType* cobject, const Glib::RefPtr<Gtk::Builder>& refBuilder)
+   * : Glib::ObjectBase("MyDialog"), // The GType name will be gtkmm__CustomObject_MyDialog
+   *   Gtk::Dialog(cobject) // Calls the base class constructor
+   *   m_my_property(*this, "my-property")
+   * @endcode
+   *
    * @param builder The Gtk::Builder from which to get the widget.
    * @param name The name of the widget.
    * @param args Additional arguments to pass to the constructor of the derived class.