Scope question: "table selection" regions?

In discussion about how to save Glue selections, @eteq raised the possibility of serializing data selection. Currently, `regions` is only intended to identify regions on the sky and maybe associated with spectral depth. Maybe we want to be able to serialize region selections associated with table columns? I think that sort of selection would fall under `astropy.regions` eventually, but we probably don't want to expand the scope of this repository just yet.