Mechanism for optional features

It's come up a number of times in our discussions as a working group: We would like to have optional features that can be adopted and if adopted by a server/client then that section of the spec can be applied. I believe we need a mechanism for this.

1. **Documentation:** we need to add a section to help organize and specify these optional features
2. **Communication:** Servers need to communicate which features they support and clients need to communicate what features they wish to use.

I know we wish to leave many of the optional features to be defined after the 1.0 release, but I'm wondering whether the mechanism should/could be put in place for the 1.0 release, so that we have a firm foundation and clear runway after the 1.0 to start building extensions and optional features.

I'm interested in hearing (1) opinions on 1.0 or post 1.0 release and (2) ideas about possible solutions for the **2. Communication** mechanism described above.