Some place to test RDF manual authoring?

It’s possible to create a folder-like system using different kinds of containers and define your own contains relationship, and you could access that through apps. I think though what you want is the .meta file - it, unlike the RDF for the Container is an editable file where you can put tags relating to the container and its contents. To find the location of the .meta file you should check the location header of the Container but currently, in NSS, it sill be at /container/.meta. Any tags you put in the .meta file will also be visible when you do a GET on the container. But they are only ever modifiable in the .meta file, not in the RDF of the container itself. If you’d like to see an example, see What is a .meta on NSS?.