Notifications can optionally have a type indicator. Although neither client or nor server must support this, some may choose to. Those servers implementing categories may use them to intelligently display the notification in a certain way, or group notifications of similar types.
Categories are in class.specific form. class specifies the generic type of notification, and specific specifies the more specific type of notification.
If a specific type of notification does not exist for your notification, but the generic kind does, a notification of type class is acceptable.
Third parties, when defining their own categories, should discuss the possibility of standardizing on the hint with other parties, preferably in a place such as the xdg mailing list at freedesktop.org. If it warrants a standard, it will be added to the table above. If no consensus is reached, the category should be in the form of "x-vendor.class.name."
The following table lists standard notifications as defined by this spec. More will be added in time.
Table 2. Categories
| Type | Description |
|---|---|
| "device" | A generic device-related notification that doesn't fit into any other category. |
| "device.added" | A device, such as a USB device, was added to the system. |
| "device.error" | A device had some kind of error. |
| "device.removed" | A device, such as a USB device, was removed from the system. |
| "email" | A generic e-mail-related notification that doesn't fit into any other category. |
| "email.arrived" | A new e-mail notification. |
| "email.bounced" | A notification stating that an e-mail has bounced. |
| "im" | A generic instant message-related notification that doesn't fit into any other category. |
| "im.error" | An instant message error notification. |
| "im.received" | A received instant message notification. |
| "network" | A generic network notification that doesn't fit into any other category. |
| "network.connected" | A network connection notification, such as successful sign-on to a network service. This should not be confused with device.added for new network devices. |
| "network.disconnected" | A network disconnected notification. This should not be confused with device.removed for disconnected network devices. |
| "network.error" | A network-related or connection-related error. |
| "presence" | A generic presence change notification that doesn't fit into any other category, such as going away or idle. |
| "presence.offline" | An offline presence change notification. |
| "presence.online" | An online presence change notification. |
| "transfer" | A generic file transfer or download notification that doesn't fit into any other category. |
| "transfer.complete" | A file transfer or download complete notification. |
| "transfer.error" | A file transfer or download error. |