Is "walk in closet" defined in the code? I've been treating them as ordinary rooms, if they have doors between them and the adjacent room. Plugs may be required by code and arc-fault protection isn't required. My thinking on the separate room issue is guided by the examples described in 26-712(f) and Appendix B 26-700(11).
However, I usually use the arc-fault circuit to feed that plug, because that circuit is already in the area. I just don't think the classification extends though a door, or hall plugs would have arc-fault protection.
