In App Notifications
Dump of notes from elsewhere. This will need writing up once we have support in GTK+.
In-application and system notifications
GNOME 3 has two basic types of notification - system notifications and in-application notifications.
System notifications communicate with the user through a combination of system banners, lock screen notifications, and the Message Tray. System notifications can be used to inform the user about events that have occurred while they are not using your application. An email application can use system notifications to communicate when new messages have been received, for example.
In-application notifications are displayed inside the window of your application. They can be used to communicate events or temporary state changes that cannot be displayed using the main interface of your application. An email application can use in-application notifications to inform the user that sending an email failed, for instance.