(define-g-flags "GtkDialogFlags" gtk-dialog-flags
  (:export t
   :type-initializer "gtk_dialog_flags_get_type")
  (:modal               #.(ash 1 0))
  (:destroy-with-parent #.(ash 1 1))
  (:use-header-bar      #.(ash 1 2)))  

:modal

Make the constructed dialog modal, see the gtk-window-modal function.

:destroy-with-parent

Destroy the dialog when its parent is destroyed, see the gtk-window-destroy-with-parent function.

:use-header-bar

Create the dialog with actions in the header bar instead of an action area.