text: #pragma once
  
  #include <gtk/gtk.h>
  
  #define DEMO_TYPE_WIDGET (demo_widget_get_type ())
  G_DECLARE_FINAL_TYPE (DemoWidget, demo_widget, DEMO, WIDGET, GtkWidget)
  
  GtkWidget * demo_widget_new       (void);
  
  void        demo_widget_add_child (DemoWidget *self,
                                     GtkWidget  *child);
  