no introspection annotation for GtkContainer::set-focus-child to indicate optional parameter
Submitted by Phil Clayton
The first parameter of GtkContainer::set-focus-child (of type GtkWidget) is optional. However, there is no introspection annotation indicating this.
This may be the case for GtkContainer::add and GtkContainer::remove signals too.
Currently, none of the four GtkContainer signals have a gtk-doc comment, so cannot include introspection annotations.