Looking for information on adding a Subject Scheme object in SDL Tridion Docs.

I'm looking for information on adding a SubjectScheme doctype to SDL Tridion Docs.

<!DOCTYPE subjectScheme PUBLIC "-//OASIS//DTD Subject Scheme Map//EN" "map.dtd">

Any pointers or references to others doing this would be much appreciated. We're planning on leveraging a subscheme for metadata values in our publication ditamaps.

 

Thanks.