It's clear that we have 4 kinds of guides emerging:

1 National / realm base guides
2 Domain guides - specify content models
3 Exchange agreements - actual exchange contents
4 System Documentation

There's some lack of clarity in people's minds about this, and mixing between #1, #2, and #3 in ways that discourage proper re-use. Adding ImplementationGuide.kind to indicate the nature of the guide will help clarify people's minds.