Bindings in testgtk.c-> doc's

["Webillo Disperso" <webillo mi madritel es>]

Hi. I'm fairly new to GTK.

testgtk.c is a file usually mentioned as being a long example about many of GTK widgets and things that can 
be done with them, and how.

On its main(), the following lines appear:
  GtkBindingSet *binding_set;
 .....
  /* bindings test
   */
  binding_set = gtk_binding_set_by_class (gtk_type_class (GTK_TYPE_WIDGET));
  gtk_binding_entry_add_signal (binding_set,
    '9', GDK_CONTROL_MASK | GDK_RELEASE_MASK,
    "debug_msg",
    1,
    GTK_TYPE_STRING, "GtkWidgetClass <ctrl><release>9 test");
 .....

Questions:
-What are they for?
-What should be noticed if commenting them?
-Some explanation about 'gtk_binding_set_by_class()' and 'gtk_binding_entry_add_signal()', or where are they 
documented? I couldn't find anything.

TIA.