What are side channel notifications in Android?

Question

The class android.support.v4.app.NotificationManagerCompat in the support library referers to Side Channel Notifications. But there is no documentation available anywhere about them.

What is the purpose of these notifications and how to use them? Can they be used for IPC?

Answer 1

Disclaimer I had to do some archeology, and can only give a guess answer based on #cef09fe (Change-Id: I9d0a572c84da0e83aac54b896fd669ce58f58739).

Grouped Notifications were added in Android 4.4 Kitkat Watch (API level 20). Grouped notifications may display in a cluster or stack on devices which support such rendering.

And my guess is that side channel is a way for AppCompat to support this when the framework NotificationManager doesn't.

So basically, you shouldn't care about this if you are targeting devices on KitKat Watch (API 20) or later.