So, you're looking for a way to include a "schema" association in the feed, and you want a standard way to do it. The only processors that will do anything useful with this information are those that know about the "profile".
<feed ...> <head> <ex:MyPetSchema>GottaHaveCategories</ex:MyPetSchema> </head> ... </feed>
I don't see the value in this in that it opens up the possibility that every extension that wants to change the containment requirements could do so in some different way. It doesn't provide any guidance on how to change those requirements in a backwards compatible way, nor does it help figure out how to reconcile a situation in which multiple such extensions are applied to the same feed/entry. Further, the core spec still does not expressly allow extensions to change the containment requirements. Thus far, the only thing an extension can do is add new types of namespace qualified metadata elements.
You're using Atom, and processors who know about your additional requirements will know about your schema. What you're asking is for the spec to lend weight to your extensions, and I'm not very positive about that.
No, what I'm asking for is a single, consistent way of declaring the use of profiles and the ability to make containment requirements independent of the element definitions. The spec is not lending weight to anything but its own core profile.
Robert Sayre
