This PR includes the documentation of the virtual option for those types which make sense to use with this option. When this is merged upstream, part two of #1387 can be appproached by adding the mapped documentation to the 2.1 branch.
Documenting the virtual option for types where it makes sense.
There is a little typo here: usefull -> useful
[#2401] Fixing a typo thanks to @michaelperrin and adding a reference…
Awesome start on this - I've already merged 2.0 into 2.1 so that you're open to continue when you can.