What does "messages" mean in the Priority Only settings in Do Not Disturb? In the DND (Do Not Disturb) settings in Android 8.1 there is an option to allow "Priority Only" notifications through. You can set what types of things qualify for priority (e.g., someone calling twice in a 15 minute period).

One of the options there is "Messages" which you can set to anyone, contacts only, starred contacts only or none.

However, what "messages" does this apply to? Is it only from hangouts or the builting messaging app? Is it SMS messages?

For example, I'd like WhatsApp messages from certainly people to come through, but I doubt Android knows how to match up the sending of a message from a third-party messaging to my contacts list?
I checked this about an year ago when I had hangouts installed

All messages (including text) that use GCM were blocked. WhatsApp doesn't use GCM so they will be received