Table Slices?

In the Slice Option modal, there's a Slice Type for "Table", but it's always greyed out. The documentation also mentions a "Table" content type, but it doesn't explain what it's for.

I'm hoping it's a feature, similar to the old ImageReady one, where we can group slices into Tables that get exported as nested HTML using Save for Web...

Does anyone know how to activate the option?