The JSON schema is used for region serialization to string?
In that case can you also show an example or two for a region JSON string and not only a schema example?

Are we inventing our own region format or is there some reference for this?
At the moment I think [`ds9` regions](http://spiff.rit.edu/tass/ds9/region.html) are very much in use ... do we want to support them somehow, maybe by a `from_ds9` parser or something?