$ zenity --help-notification Usage: zenity [OPTION…] Notification icon options --notification Display notification --text=TEXT Set the notification text --listen Listen for commands on stdin --hint=TEXT Set the notification hints The man page should mention the --hint option (while it does not) and explain how to use it, at the very least by making reference to https://www.galago-project.org/specs/notification/0.9/x344.html