What does "Ignore messages like this" do? How do I see what I've ignored?

When I tap and hold on a notification in the notifications list, I get an option to "Ignore messages like this." I can't find any explanation, though, of what this means. Does it really mean, ignore all notifications from this app? Or does it mean, only ignore messages like this one from this app? (i.e. can one app have multiple "channels" or types of notifications?)

And the other side of this - where can I see what messages I have chosen to ignore, and possibly undo it, if I once again want certain messages?