Features draft updates

[James M Snell <jasnell@xxxxxxxxx>]

Just wanted to summarize the significant changes in the current Features
draft:

 http://www.ietf.org/internet-drafts/draft-snell-atompub-feature-08.txt

 * There are four support status levels:
   * supported: client MAY use the feature
   * preferred: client SHOULD use the feature
   * required: a client that does not understand the feature SHOULD NOT
     attempt to interact with the server.  Note that this is
     purposefully not a MUST.  We're not saying that the client MUST
     use the feature, we're saying that clients that do not understand
     the feature should not attempt to interact with the server.
   * unsupported: client SHOULD NOT use the feature

   Any other value MUST be interpreted as "supported".

 * Explicitly call out that not all status levels are relevant for all
   features

 * A note is added warning implementors away from adding required
   features to existing collections.  The preference would be to
   use "preferred" instead of "required"

 * Clients SHOULD use preferred features when specified

 * Added language addressing "contradictory features", e.g. a service
   document specifying that xhtml and html titles are both required
   is contradictory.

 * Recommend that service documents containing required features contain
   an xml signature.

 * Explicitly deal with extensions to the features namespace

 * Add support levels and contradictions to the iana registry

 * Add Summary feature to indicate a servers support for the
   atom:summary element

 * Add Scheduling Publishing feature to indicate a servers support for
   manually setting the value of atom:published to control when the
   entry is made publicly available.

Still to do: Apparently some of the normative references are out of
date. I will tweak those in the next update.

- James