[gtk/gtk-3-24] overlay: Clarify pass-through docs

[Matthias Clasen <matthiasc src gnome org>]

commit 3aa742d715b5860099f07bb5600110623f666950
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Apr 16 11:14:18 2021 -0400

    overlay: Clarify pass-through docs
    
    Explain that widgets with their own windows need to
    have gdk_window_set_pass_through called on them.
    
    Fixes: #3861

 gtk/gtkoverlay.c | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/gtk/gtkoverlay.c b/gtk/gtkoverlay.c
index 8dcaaf0ab7..ae27021663 100644
--- a/gtk/gtkoverlay.c
+++ b/gtk/gtkoverlay.c
@@ -777,6 +777,11 @@ gtk_overlay_class_init (GtkOverlayClass *klass)
    * Whether to pass input through the overlay child to the main child.
    * (Of course, this has no effect when set on the main child itself.)
    *
+   * Note that this is implemented by calling gdk_window_set_pass_through()
+   * on the window that the overlay child is placed in. If the descendents
+   * of the overlay child have their own windows, you need to manually call
+   * that function on them to achieve the desired effect.
+   *
    * Since: 3.18
    */
   gtk_container_class_install_child_property (container_class, CHILD_PROP_PASS_THROUGH,