Makes all newly-created widgets as composite children until
the corresponding gtk_widget_pop_composite_child() call.
A composite child is a child that's an implementation detail of the
container it's inside and should not be visible to people using the
container. Composite children aren't treated differently by GTK (but
see gtk_container_foreach() vs. gtk_container_forall()), but e.g. GUI
builders might want to treat them in a different way.
Makes all newly-created widgets as composite children until the corresponding gtk_widget_pop_composite_child() call. A composite child is a child that's an implementation detail of the container it's inside and should not be visible to people using the container. Composite children aren't treated differently by GTK (but see gtk_container_foreach() vs. gtk_container_forall()), but e.g. GUI builders might want to treat them in a different way.