What is an empty interface used for

Question

I am looking at nServiceBus and came over this interface

namespace NServiceBus
{
    public interface IMessage
    {
    }
}

What is the us

Answer 1

In Java, empty interfaces were usually used for "tagging" classes - these days annotations would normally be used.

It's just a way of adding a bit of metadata to a class saying, "This class is suitable for kind of use" even when no common members will be involved.