The "New Context" UI on the playground is confusing. It's unclear to people what its purpose is -- especially to newcomers. The initial UI on the playground should probably just have a simple "JSON-LD validator UI". Maybe some directions could be given there to ask the user if they'd like to see how their JSON-LD looks when it's expanded (directing them to the expansion tab). If we could cleanly get more links to areas in the spec that explain what each tab means, etc. that would be helpful.

There should be some other UI element (tab/button/etc) that can be triggered to go into a "transform" mode/screen. That would make it more clear that you can use the playground to transform your JSON-LD input from one context (or none) to another. We could also have something that's a bit more directed for "adding context" to existing JSON (so JSON input box + the context to add = the result). Something that better explains, visually and interactively, what's going on with JSON-LD and what it brings to the table.

cc: @bollwyvl