possible inconsistency in metadata spec

I'm looking at the 15-March-2005 "Metadata for the OASIS Security  
Assertion Markup Language (SAML) V2.0" and noticed that there appears  
to be an inconsistency as follows:

Section 2.3 "Root Elements" restricts the root elements in a metadata  
document to either EntityDescriptor or EntitiesDescriptor.

However, Appendix A "Registration of MIME media type application/ 
samlmetadata+xml" appears to permit, in addition,  
AffiliationDescriptor as a root element.

I think the latter seems like a mistake, unless I'm just  
misunderstanding something.

The most recent errata document I have access to (22 May 2007) doesn't  
appear to have anything to say about this.

Comments?  Enlightenment?

	-- Ian