Now you can push to a set of tags in the New Composer. Rather than having to first create a segment, you can select them in the same message composer. Push to tags is still represented in our new Composer and API as a type of audience segment. You can choose an existing segment, or a tag segment you create on the fly:
This is a change in behavior from the old Push and Rich Push composers, where you had to first create a segment in the Segments area of the UI.
When you click tags, you can use our type-ahead search to combine existing tags, the same way you combine segments today.
When you select multiple tags, the devices matching those tags are combined (logical OR), which increases the audience size.