Menus are documented here.
The toolbar is documented here.
The main window displays a list of the top-level Gtk+ and GNOME windows that are defined for the current project. This includes:
GtkWindow
GtkDialog
GtkFileSelection
GtkColorSelectionDialog
GtkFontSelectionDialog
GtkInputDialog
GnomeApp
GnomeDialog
GnomeMessageBox
GnomeAbout
GnomePropertyBox